UNIVERSITY  OF  CALIFORNIA 

ANDREW 

SMITH 

HALLIDIL: 


Long -Distance  Electric 
Power  Transmission 

Being  a  Treatise  on  the 

Hydro-Electric  Generation  of  Energy; 

Its 

Transformation,   Transmission,  and 
Distribution 


BY 


ROLLIN    W.  HUTCHINSON,  JR. 

CONSULTING  ELECTRICAL  ENGINEER  ;   ASSOCIATE  MEMBER  AMERICAN  INSTITUTE 

OF  ELECTRICAL  ENGINEERS,  AND  MEMBER  OF  THE  AMERICAN 

ELECTROCHEMICAL  SOCIETY 


NEW  YORK: 

D.  VAN    NOSTRAND    COMPANY 

23   MURRAY  AND   27    WARREN   STS. 
1907 


HAUIE'E 


Copyright,  1907, 
BY  D.  VAN   NOSTRAND   COMPANY 


PREFACE 

SINCE  the  beginning  of  the  twentieth  century  the  devel- 
opment .of  water-powers  for  long-distance  transmission 
which  began  with  the  famous  Frankfort-Lauffen  trans- 
mission in  Germany,  in  1891,  has  been  so  rapid,  and  has 
been  marked  by  such  startling  feats  of  engineering  skill, 
that  it  is  almost  impossible,  except  to  those  who  have  been 
intimately  connected  with  this  field  of  engineering,  to  have 
more  than  a  vague  knowledge  of  the  physical  features  of 
such  plants. 

The  author  has  been  encouraged  to  write  the  book  by 
the  demand  of  engineers  and  students  for  information  in 
concise  and  convenient  form,  on  the  kinds  of  machinery 
and  apparatus  used  in  hydro-electric,  high-tension  engineer- 
ing, and  the  construction  and  operation  of  high-potential 
transmission  properties.  While  primarily  intended  as  a 
book  of  reference  for  engineers  and  a  text-book  for  students, 
it  is  believed  that  with  the  exception  of  some  portions  it 
can  be  intelligently  read  by  those  educated  persons  who 
are  seriously  looking  for  information  on  this  fascinating 
branch  of  applied  science.  The  book  does  not  claim  to 
present  anything  new,  nor  does  it  claim  to  be  an  exhaustive 
treatise  on  the  subject.  Indeed,  the  field  of  high-tension 
power  transmission  is  so  large  that  it  is  impossible  to  give 
more  than  a  resume  of  the  subject  within  the  compass  of 
this  work. 

The  first  three  chapters  are  devoted  to  a  brief  discussion 
of  the  salient  principles  involved  in  the  construction  and 

iii 

158898 


iv  PREFACE 

operation  of  the  hydraulic  end  of  high-tension  generating 
plants.  Elementary  mathematics  is  employed,  and  fre- 
quent reference  has  been  made  to  the  classic  of  Merriman, 
"Hydraulics." 

In  the  chapters  on  generators  and  the  laws  involved  in 
transmission,  the  treatment  is  rather  succinct,  and  presup- 
poses a  knowledge  of  alternating  currents  and  polyphase 
machinery. 

The  art  is  undergoing  such  a  rapid  evolution  that  the 
author  will  warmly  appreciate  any  suggestions  from 
readers  on  improvements  in  apparatus  treated  since  the 
material  was  prepared. 

To  those  manufacturers  who  have  courteously  given 
information  on,  and  loaned  electrotypes  of,  their  apparatus, 
the  author  desires  to  express  his  hearty  thanks. 

Chicago,  August,  1906. 


ERRATA 

PAGE  114.  Read  "several  curves  of  an  i85o-k.w.  machine.'1 

PAGE  164.  Read  L  =  ^,    L  =  d~  - 

PAGE  208.  Read  "  five  kilobits,"  "  fifty  kilovolts." 

PAGE  258.  "  Three  kilovolts  "  should  read '.  "  thirty  kilovolts." 

PAGE  317.  Omit  "  per  annum,"  second  line  from  bottom  of  page. 

PAGES  322,  323,  324.  All  values  expressed  in  kilovolts  should  read 
ten  times  larger;  thus,  "four  kilovolts"  should  be  "forty  kilovolts," 
"five  kilovolts"  should  be  "fifty  kilovolts,"  etc. 


CONTENTS 

CHAPTER  PAGE 

I.     LAWS  OF  HYDRAULICS ......  i 

II.    APPLIED  HYDRAULICS 23 

III.  HYDRAULIC  MACHINES  AND  ACCESSORY  APPARATUS.....  65 

IV.  GENERATORS,  SWITCHES,  AND  PROTECTIVE  DEVICES 109 

V.     LAWS  GOVERNING  TRANSMISSION  OF  ENERGY 159 

VI.    THE  TRANSMISSION  LINE 178 

VII.    TRANSFORMERS 239 

VIII.     MOTORS 266 

IX.     CONVERTERS 291 

X.     PRACTICAL  PLANTS 311 

XI.    DISTINCTIVE  FEATURES  OF   PROMINENT    LONG-DISTANCE 

TRANSMISSIONS 326 


LONG-DISTANCE    ELECTRIC 
POWER    TRANSMISSION 


CHAPTER    I 
LAWS  OF  HYDRAULICS 

THE  energy  of  water  is  usually  expressed  in  two  ways ; 
namely,  potential  energy  and  kinetic  energy.  Water 
weighing  W  pounds  raised  to  a  height  h  contains  an  amount 
of  potential  energy  equal  to  the  product  of  the  two  com- 
ponents, thus, 

Wh  =•  Potential  energy. 

When  a  volume  of  water  is  dropped  from  a  known  height, 
it  acquires  an  amount  of  kinetic  energy  proportional  to  the 
square  of  the  velocity  attained  by  it  in  falling ;  thus, 

v2 

W  —  =  Kinetic  energy 
*g 

in  which  W  =  the  weight  of  the  water  and  v  =  the  ve- 
locity of  its  descent  in  feet  per  second. 

According  to  the  laws  of  the  conservation  of  energy  the 
potential  energy  must  equal  the  kinetic  energy,  or 

Wh=   W—',    hence  h  =— - 

2g  2g 

Head  and  Pressure.  —  The  surface  of  calm  water  is 
perpendicular  to  the  direction  of  gravitational  force.  For 


2       LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

bodies  of  water  of  small  area,  this  surface  may  be  conven- 
iently regarded  as  a  plane.  Any  distance  or  depth  meas- 
ured below  this  plane  is  termed  a  "  head."  The  head 
upon  any  point  is  its  perpendicular  depth  below  the  level 
surface. 

Call  h  the  head  and  w  the  weight  of  a  cubic  foot  of 
water.  At  a  depth  h  each  horizontal  square  unit  has  upon 
it  a  pressure  equal  to  the  weight  of  a  column  of  water  of  a 
height  //,  and  a  cross-section  of  one  square  unit,  or  wh. 
But  since  the  pressure  at  this  point  is  exerted  in  all  direc- 
tions with  the  same  intensity,  the  unit  pressure  at  the  depth 

h  is  wh.     Conversely,  the  head  for  a  unit  pressure  /  is  ~  , 

w 

hence  7       ,  ,      P 

p  =  wh  and  h  =  —  • 

w 

When  h  is  given  in  feet  and  /  in  pounds  per  square  foot 
these  equations  reduce  to  /  =  62.5  h,  and  //  =  0.016  / 
(62.5  being  the  mean  value  of  w}. 

It  is  obvious  that  head  and  pressure  are  readily  convert- 
ible, one  into  the  other.  It  is  a  common  error  to  use  one 
term  as  synonymous  in  meaning  with  the  other :  in  reality, 
each  is  proportional  to  the  other.  It  is  convenient  to  re- 
member that  one  foot  head  is  equivalent  to  a  pressure  of 
0.434  pounds  per  square  inch ;  and  that  a  pressure  of  one 
pound  per  square  inch  is  equivalent  to  a  head  of  2.304  feet. 

Laws  of  Falling  Bodies.- — In  a  perfectly  smooth,  in- 
clined channel  or  conduit,  water  would  flow  with  a  con- 
stantly increasing  velocity,  and  would,  therefore,  obey  the 
same  laws  which  govern  a  body  moving  down  an  inclined 
plane. 

A  flow  under  such  conditions  is  never  realized  in  practice, 
since  all  surfaces  over  which  water  moves  are  more  or  less 


LAWS    OF    HYDRAULICS  3 

rough.  The  motion  due  to  gravity  is  retarded  by  the  fric- 
tion between  the  water  and  the  irregular  surfaces  over 
which  it  flows  ;  hence  the  theoretical  velocities  developed 
by  the  following  equations  cannot  be  equaled  by  the  true  or 
actual  velocities. 

If  a  body  of  water  or  any  other  substance,  at  rest  above 
the  surface  of  the  earth  and  contained  in  a  vacuum,  is 
allowed  to  fall,  its  velocity  at  the  end  of  one  second  will  be 
g  feet  (the  mean  value  of  g  being  32.16)  ;  and  at  the  end  of 
t  seconds  its  velocity  will  be  the  product  of  the  two,  or 

V=gt. 

The  distance  through  which  the  body  passes  in  the  time 
t,  is  the  product  of  the  mean  velocity  J  Fand  the  number 
of  seconds,  or  h  (the  distance)  =  \  gf. 

Transposing  to  eliminate  t,  the  relations  between  dis- 
tance h  and  velocity  V  become, 

y* 
V=    V2«i  and  h  =  -- 


If  a  body  is  falling  with  a  velocity  V^  at  the  commence- 
ment of  a  period  of  time  tt  its  velocity  at  the  expiration  of 
this  time  will  be 

v*  =  Vi+gt, 

and  the  distance  through  which  it  will  fall  in  that  time  is 

h  =  vj+\gp. 
Eliminating  t  in  the  equations,  the  relations  become 

r2  =  Pi 

and 


which  equations  hold  good  irrespective  of  the  direction  of 
the  initial  velocity   Vr 


4      LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

Flow  from  Orifices.  —  If  an  opening  or  orifice  is  made 
at  any  point  in  the  base  or  sides  of  a  vessel  filled  with 
water,  the  water  issues  from  the  orifice  with  a  velocity 
which  depends  on  the  head,  the  velocity  increasing  with 
increase  of  head. 

The  law  of  the  theoretical  velocity  of  flow  is  that  enun- 
ciated by  Torricelli  in  1664,  viz  :  The  theoretical  velocity  of 
flow  from  an  orifice  is  that  which  will  be  attained  by  a 
body  falling  from  rest  in  a  vacuum  through  a  height  equal 
to  the  head  of  water  on  the  orifice. 

Hence,  regardless  of  the  plane  in  which  the  orifice  lies, 
—  whether  it  be  vertical,  horizontal  or  inclined,  —  if  the 
head  be  sufficiently  large  to  exert  practically  a  uniform 
pressure  on  all  sections  of  the  orifice,  the  equations  ex- 
pressing the  relations  are 


and 

h       V* 
h  =  —  ; 

2g 

the  first  of  which  applies  to  the  theoretical  velocity  of 
flow  that  will  be  given  by  a  definite  head  ;  the  second,  to 
the  theoretical  head  which  will  be  produced  by  a  given 
velocity.  The  latter  expression  is  usually  designated  the 
"velocity  head." 

Discharge  from  Small  Orifices.  —  In  hydromechanics  the 
word  "discharge"  is  defined  as  the  quantity  of  water 
which  flows  in  one  second  from  an  orifice,  or  pipe.  The 
theoretical  discharge  is  commonly  represented  by  the  letter 
Q,  and  is  the  discharge  as  calculated  by  ignoring  the 
retardation  due  to  frictional  resistance. 

If  every  filament  of  water  composing  the  issuing  jet  has 


LAWS    OF    HYDRAULICS  5 

the  same  velocity,  the  quantity  of  water  which  issues  in 
one  second  is  equivalent  to  the  volume  of  a  prism  having  a 
base  of  the  same  dimension  as  the  cross-section  of  the 
stream,  and  a  length  equal  to  its  velocity.  Representing 
this  area  by  a  and  the  theoretical  velocity  by  V,  the  theo- 
retical discharge  is  given  by  the  equation 


If  a  be  taken  in  square  feet  and  V  in  feet  per  second,  the 
value  of  Q  will  be  in  cubic  feet  per  second. 

If  the  orifice  be  of  small  area,  and  the  head  h  the  same 
at  all  points  of  the  opening,  the  discharge  will  be  (theoreti- 
cally) 

Q  =  a  V  =  a  \/2gh. 

This  equation  is  strictly  applicable  only  to  orifices  which 
lie  in  a  horizontal  plane  and  on  which  the  head  is  constant. 
The  error  involved  by  applying  it  to  vertical  orifices,  how- 
ever, is  less  than  one-half  of  I  per  cent  if  h  be  greater 
than  twice  the  depth  of  the  orifice.  When  the  equation  is 
applied  to  a  vertical  orifice,  h  must  be  taken  as  the  vertical 
distance  from  the  center  of  the  orifice  to  the  free  water 
surface. 

The  Energy  of  a  Jet.  —  If  a  stream  of  water  has  a  ve- 
locity V,  and  if  W  be  the  weight  of  water  per  second 
which  passes  any  given  cross-section,  the  kinetic  energy 
possessed  by  this  moving  water  is  the  same  as  will  be 
stored  up  by  a  body  falling  freely  under  the  influence  of 
gravity  through  a  height  //,  and  attaining  thereby  a  ve- 
locity V. 

Calling  E  its  kinetic  energy, 

V2 
E  =  Wh  =  W~  . 


6      LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

Hence,  if  the  quantity  of  water  passing  through  any  given 
cross-section  of  the  jet  be  constant,  the  energy  of  the  jet  is 
(theoretically)  proportional  to  the  square  of  its  velocity. 

It  is  evident  that  the  weight  W  of  the  water  may  be 
expressed  in  terms  of  the  area  or  cross-section  of  the  jet 
and  its  velocity.  Designating  the  cross-section  of  the  jet 
in  square  feet  by  the  letter  a,  and  the  weight  of  a  cubic 
foot  of  water  by  wt 

WaV* 
&  = , 

from  which  it  is  obvious  that  the  energy  or  work  which  a 
jet  is  capable  of  performing  (theoretically)  varies  as  the 
cube  of  its  velocity. 

The  energy  of  a  jet  is  always  the  same,  irrespective  of 
the  direction  in  which  it  is  moving  —  whether  horizontal, 
vertical,  or  inclined.  Its  energy  per  second  is  under  all 
conditions  Wk,  in  which  //  is  the  velocity  head  correspond- 
ing to  the  actual  velocity  V,  and  W  the  weight  of  water 
discharged  per  second.  Since  the  theoretical  velocity  V 
generally  exceeds  the  actual  velocity,  the  energy  of  a  jet 
should  never  be  calculated  from  the  theoretical  velocity. 

Impulse  and  Dynamic  Reaction  of  a  Jet.  —  If  a  jet 
delivers  W  pounds  of  water  per  second  at  a  uniform 
velocity  F,  the  motion  of  such  a  stream  may  be  considered 
as  due  to  a  constant  force  F,  which  acts  for  one  second  on 
the  weight  IV,  and  is  then  withdrawn.  During  this  inter- 
val of  time  the  velocity  of  the  water  W  increases  from  zero 
to  a  value  F,  and  the  average  velocity  is  -J  F  Therefore, 
the  work  F-  J  F  is  given  to  the  water  by  the  force  F. 

The  kinetic  energy  of   the  flowing   water  is    W —  ;  and 


LAWS   OF  HYDRAULICS  7 

by  the  law  of  the  conservation  of  energy,  the  magnitude 
of  the  constant  force  is 


which  reduces  to 

/ 
It  is  apparent  that  the  expression  W  -  is  the  same  as 

o 

that  for  momentum;  and  as  W  may  be  written  WaV 
(w  being  the  weight  of  a  unit  of  water  and  a  the  area 
of  the  orifice),  the  equation  resolves  into  the  form  : 


_  WaV* 
~~ 


and  since 


in  which  the  value  of  F  is  termed  the  impulse  of  the  jet. 
Since  the  values  of  W,  V,  and  g  are  in  pounds  and  feet  per 
second  respectively,  the  value  of  F  is  also  expressed  in 
pounds. 

In  hydromechanics  the  word  "  impulse  "  has  a  different 
meaning  from  its  definition  in  mechanics  as  the  product  of 
force  and  time. 

Since  W  in  hydraulic  computations  is  expressed  in 
pounds  per  second,  the  impulse  will  also  be  expressed  in 
pounds. 

If  any  surface,  as,  for  instance,  the  vanes  of  a  water- 
wheel,  be  placed  in  the  path  of  the  jet,  the  impulse  may 
be  considered  as  a  pressure  which  sets  up  a  rotation  of  the 
wheel. 


8      LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

If  a  jet  is  caused  to  impinge  normally  on  a  plane  it  pro- 
duces a  pressure  on  the  plane  which  corresponds  to  the  im- 
pulse F,  because  the  force  necessary  to  stop  W  pounds  of 
water  in  one  second  is  the  same  as  that  which  was  required 
to  produce  its  motion. 

Likewise,  if  a  jet,  which  is  moving  with  a  velocity  vv 
suffers  a  retardation  by  which  its  velocity  is  reduced  to  v2 
within  one  second,  the  impulse  in  the  first  second  of  time 

is  W—  >  and  in  the  next  second,  it  is  W—  - 
g  g 

The  difference  between  these  two,  or 


is  the  dynamic  pressure  developed.  Upon  this  principle  de- 
pends the  operation  of  turbines  or  other  hydraulic  machines. 

Constant  Flow  in  Smooth  Pipes.  —  When  water  flows 
through  a  pipe  of  irregular  cross-section,  every  section  of 
which  is  filled  with  water,  a  like  quantity  of  water  passes 
each  section  per  second. 

Designating  the  quantity  of  water  by  q  and  the  mean 
velocities  by  vlt  v#  and  vs  in  sections  having  areas  av  a  , 
and  as  respectively,  the  flow  is  given  by  the  equation, 

q  —  av  —  rtj  t\  +  a2  v2  +  a3vs  ... 

(The  velocities  in  different  sections  vary  inversely  as  the 
areas  of  the  sections.) 

Call  W  the  weight  of  water  which  flows  per  second 
through  the  sections  of  the  pipe  al  and  a2,  and  let  i\  and 
v2  be  the  mean  velocities  in  these  sections.  In  the  section 
#!  the  potential  energy  possessed  by  the  water  when  at  rest 
is  Wh.  When  motion  is  imparted  to  it,  the  energy  in  that 


LAWS    OF    HYDRAULICS  9 

section  is  the  potential  energy  Wh,  due  to  the  head  pres- 
sure plus  the  kinetic  energy 


Ignoring  the  losses  due  to  impact  or  friction,  the  energy 
in  both  cases  is  the  same,  hence, 

ffl  =  ^  +  ^  and  Hz  =  hz  +  ^-> 

H  being  the  hydrostatic  head  at  no  flow.  The  law  repre- 
sented by  this  equation  was  first  established  by  Bernouilli, 
and  may  be  stated  as  follows  : 

At  any  section  of  a  tube  or  pipe,  in  which  the  flow  is 
steady  and  frictionless,  the  pressure  head  plus  the  velocity 
head  equals  the  hydrostatic  head  which  exists  when  there 
is  no  flow. 

In  applied  hydraulics  this  theorem  is  of  very  great  im- 
portance. 

Definitions  of  Coefficients  of  Contraction,  Velocity,  and 
Discharge.  —  A  jet  of  water  issuing  from  an  orifice  suffers 
a  contraction  of  area,  due  to  the  fact  that  the  filaments 
of  water  approaching  the  orifice  move  along  constantly 
converging  lines. 

This  convergence  continues  for  a  slight  distance  beyond 
the  plane  of  the  orifice. 

The  contraction  of  the  jet  causes  only  the  inner  corner 
of  the  orifice  to  be  struck  by  the  issuing  water.  (It  is 
this  phenomenon  which  causes  a  jet  issuing  from  a  cylin- 
drical orifice  to  have  the  appearance  of  a  clear  crystal  bar.) 
A  contraction  of  the  issuing  stream  also  takes  place  when 
an  irregular  or  triangular  orifice  is  used 


10     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  coefficient  of  contraction  may  be  defined  as  the 
number  by  which  the  area  of  the  orifice  must  be  multiplied 
to  give  the  area  of  a  section  of  the  jet  at  a  distance  from 
the  plane  of  the  orifice  equal  to  approximately  one-half  its 
diameter. 

Denoting  the  coefficient  of  contraction  by  cc  and  the 
area  of  the  contracted  section  of  the  issuing  jet  by  ac,  then 

ac  =  cca, 
the  value  of  which  is  always  less  than  unity. 

The  coefficient  of  contraction  can  be  directly  determined 
by  measuring  with  calipers  the  dimensions  of  the  least 


Fig.  i.     Measurement  of  Coefficient  of  Contraction 


cross-section  of  the  jet.  Fig.  i  shows  the  method  of  mak- 
ing the  measurement.  For  a  circular  orifice  having  diam- 
eters for  sections  a  and  ac,  d  and  dc  respectively, 

<d: 


A  common  mean  value  for  the  coefficient  of  contraction 
is  0.62,  which  means  that  the  minimum  cross-section  of  the 
jet  is  62  per  cent  of  that  of  the  orifice. 

The  coefficient  of  velocity  is  the  constant  by  which  the 
theoretical  velocity  of  flow  from  the  orifice  must  be  multi- 


LAWS    OF    HYDRAULICS  II 

plied  in  order  to  give  the  true  velocity  at  the  smallest 
cross-section  of  the  jet. 

Let  cv  be  the  coefficient  of  velocity,  V  the  theoretical 
velocity  due  to  the  head,  and  v  the  actual  velocity  at  the 
contracted  section,  then, 

V  '  —  cvv  —  cv  ^2gh. 

The  coefficient  of  velocity  is  always  less  than  unity,  since 
it  is  impossible  for  gravitational  force  to  generate  a  velocity 
greater  than  that  due  to  the  head. 

A  mean  value  that  is  commonly  employed  is  0.98,  which 
means  that  the  actual  velocity  of  flow  at  the  contracted 
section  is  98  per  cent  of  the  theoretical  velocity. 

The  coefficient  of  discharge  is  the  constant  by  which  the 
theoretic  discharge  must  be  multiplied  in  order  to  give  the 
actual  discharge. 

Calling  cd  the  coefficient  of  discharge,  Q  the  theoretical 
and  q  the  actual  discharge  per  second,  then, 

q  =  cdQ. 

The  coefficient  of  discharge  may  be  accurately  deter- 
mined by  permitting  the  flow  from  an  orifice  to  fall  into  a 
receptacle  having  a  constant  cross-section,  and  measuring 
the  height  of  water  by  a  hook  gauge. 

Then  q  being  determined  and  Q  calculated  from  the 
formula  for  theoretic  quantity, 


Influence    of    Suppression  of   the  Contraction.  —  If  the 

lower  edge  of  a  vertical  orifice  is  near  the  bottom  of  a 
reservoir,  the  issuing  filaments  of  water  from  its  lower  por- 
tion travel  in  lines  almost  perpendicular  to  the  plane  of  the 
opening,  and  hence  there  is  no  contraction  of  the  jet  on 


12     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

the  lower  part.     This  phenomenon  is  termed  suppression 
of  the  contraction.     It  also  occurs  when  the  lower  edge  of 


Fig.  a.     Suppression  of  Contraction  of  Jets 

the  orifice  is  slightly  above  the  bottom,  as  shown  in  Fig.  2, 
but  is  smaller  in  this  case. 

Should  the  orifice  be  located  so  that  one  of  its  vertical 
edges  is  at  or  near  the  side  of  a  reservoir,  as  at  5,  the  jet 
has  its  contraction  suppressed  on  only  one  side. 

If  one  of  the  vertical  edges  of  an  orifice  is  located  at  the 
lower  corner  of  a  reservoir,  the  jet  is  suppressed  in  its 
tendency  to  contract  both  upon  one  side  and  upon  its  lower 
portion. 

Suppression  of  the  contraction  of  a  jet  is  undesirable 
since  it  increases  the  cross-section  of  the  jet  at  a  point 
where  complete  contraction  would  otherwise  occur.  This 
increases  the  discharge  to  an  extent  depending  on  whether 
the  suppression  takes  place  on  one  or  two  sides. 

Lesbros  and  Bidone  have  shown  that  for  square  orifices, 
with  contraction  suppressed  on  one  side,  the  coefficient  of 


LAWS    OF   HYDRAULICS  13 

discharge  is  increased  nearly  3.5  per  cent;  with  contrac- 
tions suppressed  on  both  sides  nearly  7.5  per  cent. 

For  rectangular  orifices  the  increase  in  the  coefficient  of 
discharge  from  this  cause  varies  from  6  to  12  per  cent, 
depending  upon  the  ratio  of  length  to  height. 

Flow  from  Circular  Vertical  Orifices.  —  If  a  circular 
vertical  orifice  of  a  diameter  d,  discharges  water  which 
has  a  head  h  on  the  center  of  the  orifice,  then  the  mean 
velocity  (theoretical)  =  \/2gh  ;  and  the  theoretical  discharge 
(Q  =  av)  is 


which  is  only  applicable  when  h  is  quite  large  compared 
with  d. 

Flow  from  Rectangular  and  Square  Vertical  Orifices.  — 
When  the  dimensions  of  an  orifice  in  the  side  of  a  chamber 
filled  with  water  are  small  as  compared  with  the  head,  the 


velocity  of  outflow  is  ^2gh,  h  being  the  head  on  the 
center  of  the  opening. 

Under  such  conditions  the  theoretical  discharge  from  a 
rectangular  vertical  orifice  is 

Q  =  bd\/2ght 

in  which  b  is  the  width  and  d  the  depth  of  the  orifice.  In 
general,  the  equation  for  actual  flow  from  a  square  vertical 
orifice  is 

q  =  c^  V^  =  8.02  cdP  V^ 

in  which  cd  is  the  coefficient  of  discharge  and  b  is  the  side 
of  the  square. 


14     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

In  case  h  is  smaller  than  about  twice  the  side  of  the 
orifice,  the  formula  for  accurate  determination  of  q  is 

q  =  5-347  cb(h?-h$)\ 

and  since  the  linear  dimensions  are  in  feet,  the  value  of  q 
will  be  in  cubic  feet  per  second. 

Measurement  of  Water  by  Orifices.  —  The  use  of  orifices 
for  accurately  measuring  water  demands  many  precau- 
tions. It  is  essential  in  the  first  place  that  the  area  of  the 
orifice  be  small  compared  with  the  area  of  the  reservoir ; 
otherwise  an  error  is  introduced  due  to  velocity  of  approach. 

The  inside  edge  of  the  orifice  should  have  a  right-angled 
corner  of  definite  dimensions,  which  must  be  accurately 
ascertained.  When  the  orifice  is  cut  in  wood  it  is  impera- 
tive that  the  inside  surfaces  be  perfectly  smooth  and 
unobstructed  with  slime.  It  is  especially  inadvisable  to 
use  orifices  under  small  heads,  since  slight  changes  in  the 
head  occasion  considerable  errors  in  computation.  The 
coefficients  of  discharge  under  such  conditions  also  vary 
quite  quickly, 

Should  the  head  on  the  orifice  be  very  low,  determina- 
tions of  the  discharge  are  untrustworthy,  owing  to  the 
vortices  which  are  set  up. 

Precise  measurements  of  the  head  can  only  be  made 
with  the  hook  gauge. 

Weirs.  —  A  weir  may  be  defined  as  an  opening  cut  in 
the  top  edge  of  the  vertical  side  of  a  vessel,  through 
which  water  issues.  The  opening  is  usually  of  rectangular 
shape,  and,  unless  otherwise  stated,  a  weir  may  always  be 
assumed  to  have  such  a  shape  that  the  lower  edge  is  truly 
horizontal  and  the  sides  vertical.  The  term  "crest"  is 
applied  to  the  horizontal  edge  of  the  weir. 


LAWS    OF    HYDRAULICS  15 

Weirs   are    separated    into    two   general  classes :  weirs 
with  end  contractions  and  those  without  such  contractions. 


Fig.  3.    Weir  with  Contracted  Ends. 

Fig.  3  shows  the  more  common  type  of  weir,  with  the  ends 
contracted.  In  this  form  the  vertical  sides  of  the  opening 
are  cut  away  a  sufficient  distance  so  that  both  sides  of  the 
weir  are  thoroughly  contracted. 

In  Fig.  4  the  edges  of  the   opening  coincide  with  the 
sides  of  the  feeding  trough,  which  causes  the  filaments  of 


Fig.  4.    Weir  without  Contracted  Ends. 

water  against  the  sides  to  pass  over  the  crest  without  suf- 
fering deflection  from  the  perpendicular  planes  in  which 
they  are  moving. 


1 6      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

In  order  to  obviate  error  due  to  suppression  of  the  con- 
traction, the  distance  from  the  crest  of  a  weir  to  the  bottom 
of  the  supplying  channel  or  reservoir  should  be  three  times 
the  head  of  water  on  the  crest.  This  rule  is  also  applicable 
to  weirs  with  end  contractions. 

Weirs  are  extensively  used  in  determining  the  flow  of 
small  streams  and  for  ascertaining  the  quantity  of  water 
delivered  to  hydraulic  motors. 

On  account  of  the  smallness  of  the  head  on  the  crest  of 
the  weir,  it  is  essential  to  determine  it  with  accuracy  in 
order  to  obviate  an  error  in  the  calculated  discharge.  To 
ascertain  the  head  on  the  crest  of  the  weir,  the  measure- 


Fig.  5.    Method  of  Making  Weir  Measurement  of  Streams 

ment  is  taken  several  feet  up  stream,  as  indicated  in  Fig. 
5,  in  order  to  prevent  the  error  which  the  curve  taken  by 
the  surface  of  the  water  introduces. 
Various  conditions  of  flow  and  surface  contour  determine 


LAWS    OF    HYDRAULICS  I/ 

the  distance  up  stream  to  which  the  curve  will  extend.  As 
a  general  thing,  level  water  is  to  be  had  at  a  distance  of 
about  3  feet  from  the  crest  of  the  weir,  in  case  the 
weir  is  a  small  one.  If  the  weir  is  large,  the  length  of  the 
curve  from  the  crest  up  stream  varies  from  5  to  9  leet. 

In  the  majority  of  observations  to  determine  the  dis- 
charge of  weirs,  the  water  possesses  a  considerable  velocity 
of  approach  at  the  point  where  the  head  //is  recorded  by 
the  hook  gauge. 

Call  v  the  velocity  in  the  supplying  canal  at  this  point 
(Fig.  5),  and  consider  such  velocity  as  being  due  to  a  head 
h  from  a  body  of  calm  water  some  distance  up  stream  from 
the  recording  instrument.  Evidently  the  actual  head  on 
the  crest  is  H  4-  //,  since  the  measuring  device  would  have 
recorded  such  a  value  if  it  had  been  located  at  a  point 
where  the  velocity  was  nil. 

Hence  the  discharge  Q  is  (theoretically) 


where  H  is  the  reading  of  the  gauge,  and  h  is  a  value  to  be 
computed  from  the  velocity  v. 

Both  the  contraction  of  the  stream  and  the  friction  of  the 
weir  edges  modify  this  equation  appreciably,  so  that  the  ex- 
pression giving  the  actual  discharge  becomes  : 


in  which  s  is  a  constant,  the  value  of  which  ranges  from 
i.o  to  1.5. 

If  the  ends  of  the  weir  are  contracted,  and  if  the  velocity 
of  approach  is  zero,  the  discharge  per  second  is 


1  8     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

In  case  there  is  a  velocity  of  approach   v  at  the  recording 
device,  the  expression  giving  the  discharge  becomes  : 

b(H+  1.4*)  i 


Hydraulic  Measuring  Instruments.  —  The  instruments 
commonly  used  in  hydraulic  measurements  are  the  hook 
gauge,  the  piezometer  or  pressure  gauge,  the  differential 
pressure  gauge,  the  current  meter,  the  water  meter,  the  steel 
tape,  level  and  transit. 

The  hook  gauge  consists  of  a  graduated  metallic  rod  mov- 
ing in  a  vertical  plane  in  fixed  supports,  and  fitted  with  a 
vernier  by  means  of  which  readings  can  be  made  to 
thousandths  of  a  foot.  To  the  lower  end  of  the  rod  is 
attached  a  sharp  pointed  hook  which  is  raised  or  lowered  by 
turning  the  vernier  until  the  point  of  the  hook  is  exactly  at 
the  water  level. 

In  making  readings  with  the  hook  gauge  the  point  of  the 
hook  is  lowered  slightly  below  the  surface  of  the  water  by 
actuating  the  screw  at  the  upper  part  of  the  device.  When 
the  point  has  almost  pierced  the  skin  of  the  water  surface 
a  slight  bulge  or  protuberance  manifests  itself.  To  prevent 
a  fictitious  reading  the  point  is  lowered  until  the  bubble  or 
pimple  is  just  visible  to  the  eye. 

The  principal  use  of  the  hook  gauge  is  for  ascertaining  the 
height  or  head  of  water  on  the  crest  of  a  weir.  In  such 
cases  the  heads  of  water  are  slight,  and  hence  must  be  pre- 
cisely determined.  The  most  accurate  gauges  are  gradu- 
ated to  read  in  ten  thousandths  of  a  foot.  Fig.  6  shows  a 
hook  gauge. 

,  The  piezometer  or  pressure  gauge  is  a  device  for  recording 
the  pressure  of  water  in  a  pipe.  A  common  form  of 
piezometer  consists  of  a  dial  graduated  to  read  in  pounds 


LAWS    OF    HYDRAULICS 


per  square  inch  and  fitted  with  a  movable  pointer.  Its 
principle  of  operation  is  analogous  to  the  Bourdon  steam 
gauge.  A  small  coiled  tube  closed  at  one  end  is  placed  in  a 
containing  case.  The  other  end  of  the  tube  is  joined  to  the 
opening  through 
which  the  water 
is  introduced. 
When  subjected 
to  water  pressure 
the  tendency  of 
the  tube  is  to 
straighten ;  hence 
the  closed  end 
moves,  and  by  do- 
ing so  actuates  the 
pointer  which  is 
attached  to  it. 
When  the  pressure 
is  removed  the  tube 
returns  to  its  nor- 
mal position.  If  the 
water  pressure  is 
very  high  the  Bourdon  type  of  gauge  becomes  impracticable, 
a  mercury  gauge  being  generally  employed  in  such  cases. 

A  differential  pressure  gauge,  as  the  name  implies,  is  a 
device  for  measuring  differences  of  head  or  pressure.  In 
its  simplest  form  the  instrument  consists  of  a  vertical  scale 
graduated  in  practical  fractions  and  rigidly  attached  to  a 
fixed  support.  The  water  columns,  of  which  the  heads  are 
required  to  be  determined,  are  led  by  means  of  curved  tubes 
to  the  sides  of  the  scale  and  their  differences  of  head  read 
on  the  scale, 


Fig.  6.    Hook  Gauge 


2O     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


When  the  heads  are  quite  high  a  mercury  differential 
gauge  is  employed.  This  consists  of  a  £/-tube  (open  at  the 
top)  to  which  is  joined  at  the  horizontal  part  of  the  U  a  ver- 
tical tube  (see  Fig.  7).  This  attached  tube  is  fitted  with  a 

stopcock,    as     are 
also  the    limbs    of 
Qj=[  t±(]B  the  {/-tube. 

The  uppermost 
of  the  stopcocks 
being  open,  the 
mercury  is  poured 
in  through  the  top 
(m  and  n  being 
closed).  The  mer- 
cury stands  at  the 
same  level  in  each 

E  (]  tube.    Cocks  B  and 

H  are  then  closed 
and    m  and   n  are 

Fig.  7.    Differential  Mercury  Gauge  opened.        Water 

rushes  in  through  m  and  ;/,  and  the  mercury  column  is 
lowered  in  one  tube  and  raised  in  the  other.  From  the 
difference  between  the  heights  of  the  mercury  columns  the 
differences  in  heads  are  determined.  In  mercury  gauges  of 
both  types  (the  piezometer  and  differential),  the  specific 
gravity  of  the  water  and  mercury  at  various  temperatures 
is  required  to  be  known.  The  gauges  must  also  be  cali- 
brated over  that  part  of  the  scale  where  readings  are  to  be 
made. 

The  current  meter  is  virtually  a  small  windmill  fitted  with 
several  vanes  mounted  on  a  spindle.  The  faces  of  the 
vanes  are  so  placed  that  normally  the  pressure  of  the  cur- 


LAWS   OF    HYDRAULICS 


21 


rent  is  directed  against  the  vanes  and  causes  them  to  revolve 
at  a  speed  proportional  to  the  velocity  of  the  current.  In 
very  accurate  instruments  the  number  of  revolutions  in  a 
definite  time  is  recorded  by  an  appliance  located  either 
in  a  boat  or  one  on  bank  of  the  stream.  From  the  base 
used,  wires  carrying  an  electric  current  are  led  to  the  meter 
under  water.  Electrical  con- 
nection is  made  and  broken  at 
every  revolution,  and  so  cause 
a  dial  to  be  actuated  on  the 
recording  device.  From  the 
number  of  revolutions  regis- 
tered in  a  given  time  the 
observer  computes  the  mean 
velocity  of  the  stream.  The 
Price  type  of  current  meter, 
which  is  commonly  employed 
in  America,  is  shown  in  Fig.  8. 
The  water  meter  is  a  de- 
vice for  measuring  the  quan- 
tity of  water  supplied  to  an 
hydraulic  motor  or  to  a  build- 
ing or  factory.  Meters  for  this  purpose  operate  on  the  dis- 
placement principle  ;  that  is,  water  in  passing  through  the 
meter  moves  either  a  valve  or  a  piston,  or  perhaps  a  wheel ; 
the  motion  being  transmitted  through  a  clockwork  mechan- 
ism to  dials  which  are  calibrated  to  record  the  quantity 
passed  through  in  any  given  time.  Water  meters  are  of  the 
piston  type,  screw  type,  or  rotary  type.  In  the  piston  type 
of  meter  the  flow  of  water  forces  two  pistons  to  move  in 
opposite  directions,  the  water  being  admitted  and  discharged 
through  ports  in  the  cylinder  which  are  opened  and  closed 


Fig    8.     The  Price  Current  Meter 


22      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

by  slide  valves.  The  rotary  meter  consists  of  a  wheel 
which  is  so  fitted  in  a  case  that  it  is  caused  to  rotate  when 
the  water  passes  through.  The  screw  meter  consists  of  an 
inclosed  helical  member  which  is  caused  to  revolve  on  its 
axis  by  the  entering  water. 


CHAPTER    II 
APPLIED  HYDRAULICS 

Flow  in  Streams  and  Rivers.  —  Definitions  of  Wetted 
Perimeter,  Hydraulic  Radius  and  Slope. 

Although  no  branch  of  hydraulic  engineering  has  had 
bestowed  upon  it  more  diligent  scientific  investigation  than 
that  of  the  flow  in  streams  and  river  channels,  yet  at  the 
present  time  the  subject  is  but  poorly  understood. 

The  desideratum  in  these  investigations  and  study  has 
been  the  perfection  of  a  simple  method  for  ascertaining  the 
mean  velocity  and  discharge  without  necessitating  the 
employment  of  costly  methods  of  instrument  measure- 
ments. 

The  flow  in  a  stream  or  river  is  said  to  be  steady  when 
the  same  quantity  of  water  passes  each  section  in  one  sec- 
ond. When  this  condition  is  realized,  the  mean  velocities 
in  different  sections  vary  inversely  as  the  areas  of  the  sec- 
tions. In  the  case  of  steady  flow  where  the  sections  under 
consideration  are  the  same  in  area,  the  flow  is  said  to  be 
uniform. 

When  the  stream  is  rising  or  falling,  the  flow  is  said  to 
be  non-uniform. 

The  wetted  perimeter  of  the  cross-section  of  a  chan- 
nel is  that  part  of  the  boundary  which  is  in  contact  with 
the  water.  It  is  generally  designated  by  the  letter  /. 

The  hydraulic  radius  of  the  cross-section  of  a  chan- 
nel is  its  area  divided  by  the  wetted  perimeter.  It  is 

23 


24     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

denoted  by  the  letter  r.  Calling  a  the  area  of  the  cross- 
section  of  a  channel,  the  hydraulic  radius  *•=.-• 

The  value  of  r  is  expressed  as  a  linear  quantity  in  the 
same  units  as  /.  It  is  not  infrequently  termed  the  hydrau- 
lic depth,  or  the  hydraulic  mean  depth,  since  for  a  shallow 
section  it  varies  but  slightly  from  the  mean  depth  of  the 
water. 

The  slope  of  a  water  surface  in  a  longitudinal  section 
is  the  ratio  of  the  fall  h  to  the  length  /  in  which  that  fall 
occurs.  It  is  usually  designated  by  the  letter  s.  Its  value 
is  determined  by  the  equation 

h 

S=T' 

A  precise  determination  of  its  value,  however,  involves  a 
determination  of  h.  This  is  done  by  comparing  the  water 
level  at  each  end  of  a  line  to  a  bench  mark,  using  a  hook 
gauge  or  some  other  accurate  method.  The  benches  are 
connected  by  level  lines  carefully  run  and  a  length  /  meas- 
ured along  the  inclined  channel.  This  length  should  be 
made  as  long  as  is  consistent  with  practical  conditions, 
since  the  longer  it  is  the  smaller  becomes  the  relative  error 
in  h. 

When  the  slope  is  zero  no  flow  occurs ;  but  with  even  a 
very  slight  slope  the  force  of  gravity  supplies  a  component 
acting  down  the  inclined  surface,  and  more  or  less  motion 
follows.  It  is  obvious  that  the  velocity  of  flow  increases 
with  increase  of  slope. 

Determination  of  the  Energy  of  Streams.  —  The  deter- 
mination of  the  energy  of  a  stream  involves  the  meas- 
urement of  its  velocity  of  flow  from  which  the  discharge  is 
computed  from  the  relation  q  =  av  ;  or  in  case  of  a  small 


APPLIED    HYDRAULICS  2$ 

stream  by  direct  measurements  of  the  discharge  by  means 
of  a  weir. 

When  a  dam  is  thrown  across  a  stream  of  appreciable 
size  it  is  possible  to  use  the  dam  as  a  weir,  provided  there 
is  no  seepage  of  water  through  it.  In  such  a  case  the  coeffi- 
cients in  the  equations  for  waste  weirs  are  used  in  making 
the  computations. 

In  the  absence  of  a  dam  a  method  of  gauging  is  generally 
employed.  This  is  considered  farther  along. 

In  ascertaining  the  velocity  of  flow  from  which  the  dis- 
charge is  calculated,  it  is  customary  to  employ  the  float 
method.  The  three  kinds  of  floats  used  are  termed  surface 
floats,  double  floats,  and  rod  floats. 

A  surface  float  must  be  immersed  to  such  a  depth  that  it 
will  completely  obey  the  motion  of  the  upper  filaments  ; 
and  it  should  be  of  a  form  which  is  not  easily  affected  by 
the  wind. 

A  double  float  comprises  a  surface  float  and  a  sub-surface 
float.  The  sub-surface  float  is  a  smaller  surface  float  which 
is  connected  by  means  of  a  fine  cord  or  wire  to  the  surface 
float  ;  the  surface  float  being  weighted  in  order  to  keep  it 
submerged,  and  cause  it  to  pull  the  connecting  string 
sufficiently  taut. 

It  is  essential  that  the  surface  float  be  made  of  a  shape 
that  will  offer  but  little  resistance  to  motion.  The  lower 
float  should  be  of  appreciable  size,  since  the  purpose  of  the 
combination  is  to  ascertain  the  velocity  of  the  lower  one 
only. 

While  this  method  of  double  floats  is  commonly  used,  it 
is  not  to  be  considered  an  accurate  one,  since  errors  are 
introduced  by  the  cord  friction,  and  by  the  velocity  of  the 
large  float  being  influenced  by  the  upper  one. 


26     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  rod  float  consists  of  a  hollow  cylinder  of  tin,  which  is 
weighted  to  stand  vertically  at  any  desired  depth  by  putting 
in  shot  or  pebbles.  When  a  rod  float  is  employed  for  mak- 
ing a  velocity  determination,  it  should  be  weighted  so  as  to 
sink  almost  to  the  bottom  of  the  channel. 

Velocity  observations  by  means  of  floats  are  conducted  as 
follows  :  A  definite  length  of  channel  is  marked  off,  and 
two  observers  with  stop  watches  are  stationed,  one  at  each 
end,  to  time  the  movement  of  the  float  past  each  point.  The 
use  of  one  stop  watch  is  permissible,  the  passage  of  the  float 
at  each  station  being  signaled  by  the  watchers  to  a  time- 
keeper. 

If  /represents  the  length  of  the  channel  and  t  the  time 
in  seconds  required  for  the  float  to  pass  over  the  channel 

base,  the  velocity  v  =  —  .    When  numerous  observations  are 

made,  the  work  of  division  is  lightened  by  using  the  recip- 
rocals of  the  values  of  /  and  multiplying  them  by  /,  which 
may  be  an  even  number. 

The  velocity  of  a  rod  float  is  said  to  be  the  mean  velocity 
of  all  the  filaments  of  water  in  contact  with  it  ;  but  this  is 
not  true,  because  the  rod  moves  a  trifle  slower  than  the 
water. 

The  formula  of  Francis  is  perhaps  the  best  empirical  one 
for  determining  the  mean  velocity  Vm  of  the  filaments 
between  the  surface  and  the  bed  of  a  stream  from  the 
observed  velocity  Vf  of  the  rod  float.  This  formula  is 


Vm  =  Vf  (1-012  -  o.n6)y  -^  > 

where  D  is  the  total  depth  of  the  stream,  and  /X  the  depth 
of  water  below  the  end  of  the  rod. 


APPLIED   HYDRAULICS  2/ 

A  more  accurate  method  than  floats  for  determining  the 
velocities  of  streams  is  the  use  of  the  current  meter.  This 
device  is  operated  from  a  bridge  in  the  case  of  small  streams 
or  from  an  anchored  boat  in  a  river.  This  method  of  gaug- 
ing the  discharge  gives  more  accurate  results  than  can^  be 
obtained  by  any  formula. 

For  making  a  gauging,  a  section  of  channel  should  be 
selected  where  a  uniform  flow  exists.  Several  sections  at 
right  angles  to  the  direction  of  flow  are  then  chosen,  and 
soundings  made  upon  them  at  a  number  of  points  across 
the  stream,  the  water  gauge  being  read  at  each  sounding. 
The  distance  between  sounding  points  is  measured  by 
means  of  a  cord  stretched  across  the  stream. 

The  information  is  now  at  hand  for  obtaining  the  areas 

shown  in  Fig.  9.  The 
sum  of  these  areas 
is  the  total  area  a. 

In   Order  to    obtain          Fig.  9.     Method  of  Determining  Total  Area  of 
.-,  i  T,  .         !  a  Stream 

the    additional    areas 

for  a  rise  of  stream,  levels  should  be  run  beyond  the  water 

edge  to  high-water  marks. 

When  a  current  meter  can  be  used,  it  is  necessary  to  make 
readings  only  in  one  section  :  when  floats  are  used,  two  or 
more  sections  should  be  selected. 

The  next  step  is  the  determination  of  the  mean  velocities 
vi>  vv  7;s'  etc->  m  each  °f  tne  sub-areas.  When  a  current 
meter  is  employed,  this  is  accomplished  by  commencing  at 
one  side  of  a  sub-division  and  slowly  moving  the  meter  until 
bottom  is  nearly  touched  ;  then  moving  it  a  few  feet  in  a 
horizontal  plane  and  drawing  it  to  the  surface  ;  again  mov- 
ing it  a  short  distance  longitudinally  and  lowering  it,  and  so 


28     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

on  until  the  entire  sub-area  has  been  gone  over.  The 
velocity  obtained  from  the  total  number  of  revolutions  dur- 
ing the  time  the  meter  is  submerged  is  the  mean  velocity 
for  the  sub-area. 

A  common  method  of  making  this  determination  consists 
in  merely  raising  and  lowering  the  meter  in  the  middle  of  the 
sub-area  and  taking  a  reading.  This  gives  a  fair  approxima- 
tion to  the  mean  velocity. 

The  areas  and  velocities  having  been  found,  the  discharge 
q  is  computed  by  the  equation 

q  =  a^  +  a2v2  +  aBvB  +  .  . . .  J 

dividing  this  by  the  total  area,  a,  the  mean  velocity  in  the 
entire  section  is  ascertained. 

Rough  determinations  of  velocity  can  be  found*  by  one  or 
several  measurements  by  the  use  of  floats.  This  method  is 
much  less  expensive  than  the  other  methods  given,  and 
where  quick  and  only  approximate  results  are  desired  is  to 
be  recommended. 

Experimental  work  has  shown  that  the  ratio  of  the  mean 
velocity,  v,  to  the  maximum  surface  velocity,  V,  lies  between 
0.7  and  0.85  ;  calling  it  0.8 

v  =  0.08  V. 

This  assumption  gives  an  error  in  the  value  of  v  which 
rarely  exceeds  1 8  per  cent ;  usually  the  error  is  much  less 
than  this  value. 

The  selection  of  the  particular  method  to  be  used  in 
determining  the  energy  of  streams  should  depend  upon  the 
conditions.  It  will  be  usually  found  that  measurements 
which  give  the  most  accurate  results  irrespective  of  expense 
are  the  most  satisfactory  in  the  long  run. 


APPLIED    HYDRAULICS  2Q 

Types  of  Dams.  —  Five  general  types  of  dams  are  em- 
ployed in  hydraulic  engineering  practice :  masonry  dams, 
rock-Jill  dams,  hydraulic-fill  dams,  timber  dams,  and  earthen 
dams. 

The  type  of  dam  suitable  for  any  given  condition  depends 
on  the  character  of  the  foundation  which  can  be  secured, 
the  size  and  importance  of  the  structure  which  is  necessary, 
the  topography  of  the  country,  the  degree  of  imperviousness 
required,  and  the  permissible  cost. 

The  character  of  structure  best  adapted  to  withstand 
water  pressure  and  the  destructive  action  of  the  elements  is 
unquestionably  the  masonry  dam  founded  on  solid  rock,  and 
built  up  in  the  form  of  a  monolith  between  natural  rock 
buttresses  on  a  gorge,  with  Portland  cement  mortar. 

Masonry  dams,  however,  cannot  be  erected  on  every 
site  where  it  is  desired  to  impound  water,  since  the  founda- 
tions are  not  always  suitable,  and  the  conditions  which 
must  be  met  render  their  cost  prohibitive. 

The  general  requirements  to  be  met  in  the  design  of  a 
masonry  dam  are  :  (i)  It  must  not  fail  by  overturning  ;  (2) 
it  must  not  slide  on  its  foundations  or  any  horizontal  points  ; 
(3)  it  must  not  fail  by  the  crushing  of  the  masonry  or  by 
the  settlement  of  its  foundations  ;  (4)  it  must  be  safe  from 
excessive  pressure  upon  the  masonry  whether  the  reservoir 
be  full  or  empty  ;  (5)  certain  known  safe  limits  to  crushing 
of  the  masonry  of  the  class  to  be  used  should  not  be 
exceeded. 

Masonry  dams  are  generally  built  in  the  form  of  a  sim- 
ple triangle  with  certain  modifications,  such  as  a  definite 
width  of  top  to  enable  the  dam  to  resist  wave  action  and  ice 
thrust. 

Masonry  dams  may  resist  the  thrust  of  water  pressure 


3O     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

either  by  their  weight  alone  or  by  being  built  in  the  form 
of  an  arch  which  will  transmit  the  pressure  to  the  abut- 
ments. The  first  of  these  two  types  is  called  the  "  gravity  " 
dam.  The  second  is  termed  the  "  arch  "  dam  ;  and  it  may 
be  either  of  the  gravity  type  in  arched  form,  or  it  may 
depend  upon  its  arched  form  alone. 

In  either  case,  the  weight  of  the  dam  must  be  borne  by 
foundations  which  must  be  of  the  best  quality  of  solid  bed 
rock.  Every  masonry  dam  should  be  built  in  the  form  of 
an  arch  in  order  to  avoid  cracks  or  fissures  in  its  surface  due 
to  changes  of  temperature.  Another  advantage  of  a  curved 
arch  dam  is  that  the  pressure  of  the  water  tends  to  close 
all  small  cracks  that  occur,  and  also  takes  up  the  move- 
ment due  to  temperature  changes  without  producing  cracks. 

Wilson  says  that  the  pressure  on  the  back  of  an  arched 
dam  is  perpendicular  to  the  up-stream  face  and  is  decomposed 
into  two  components,  one  perpendicular  to  the  span  of  the 
arch  and  the  other  parallel  to  it. 

Rock-fill  dams  find  application  at  the  present  time  in 
cases  where  economy  is  the  main  consideration.  They  are 
largely  used  in  the  Western  States  for  reservoir  dams  when 
a  large  supply  of  stone  is  available.  They  are  built  in  six 
forms  :  (i)  With  a  facing  of  asphalt  concrete  laid  on  a 
sloping  wall ;  (2)  with  a  central  core  of  steel  plates  and 
hand-laid  facing  walls;  (3)  with  facing  of  Portland  cement 
laid  on  a  dry  wall  ;  (4)  with  facing  of  masonry  built  verti- 
cally and  covered  on  the  lower  side  with  blocks  of  stone  laid 
in  mortar  ;  (5)  with  facing  of  steel-plates  laid  on  a  sloping 
interior  surface  on  a  dry  hand-laid  wall ;  (6)  with  a  facing 
of  earth. 

Hydraulic-fill  dams  are  the  cheapest  to  construct,  and 
are  used  in  regions  where  the  adoption  of  a  different  type 


APPLIED    HYDRAULICS  31 

would  be  prohibitive  on  account  of  the  topography  of  the 
country  and  the  cost  of  transporting  material  to  the  site. 
The  conditions  required  for  the  practical  employment  of 
hydraulic-fill  dams  are:  (i)  An  abundance  of  water  at  a 
proper  elevation  to  form  a  "sluicing  head  "  ;  (2)  sufficient 
deposits  of  materials  to  form  the  dam,  convenient  to  either 
end  and  high  enough  above  the  top  to  permit  of  the  requi- 
site grade  for  transporting  the  suspended  matter  to  the 
desired  point ;  (3)  a  good  foundation,  which  is  requisite  for 
all  dams. 

Hydraulic-fill  dams  are  constructed  by  tearing  down 
loosely  attached  rock,  earth,  and  other  organic  matter  by 
means  of  a  jet  of  water  under  high  pressure  and  allowing 
it  to  float  to  the  point  where  the  dam  is  to  be  constructed. 
They  are  commonly  employed  in  some  sections  of  the  West 
for  storage  reservoirs.  They  have  been  built  as  cheaply  as 
65  cents  per  acre-foot  of  storage  capacity. 

Wooden  dams  are  frequently  employed  when  the  stream 
is  small,  and  a  supply  of  timber  is  readily  available.  Their 
chief  recommendation  is  cheapness. 

Earthen  dams,  pure  and  simple,  are  seldom  used  at  the 
present  time.  Six  forms  exist:  (i)  A  homogeneous  em- 
bankment of  earth  in  which  all  material  is  alike  through- 
out ;  (2)  an  embankment  with  a  central  core  of  puddle  con- 
sisting generally  of  a  mixture  of  sand,  gravel,  and  concrete 
of  clay  ;  (3)  embankment  in  which  the  central  core  is  a  wall 
of  masonry  or  concrete  ;  (4)  embankment  with  "puddle" 
or  concrete  placed  on  the  water  face  ;  (5)  embankment  of 
earth  resting  against  an  embankment  of  loose  earth ;  (6) 
embankment  "  sluiced"  into  position  by  high  pressure.  The 
most  popular  of  these  forms  is  the  masonry  core  wall  with 
"puddle  "  facing. 


32     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


Pressure  on  Dams.  Causes  of  Failure.  —  In  construct- 
ing a  dam  to  impound  water  one  of  two  possible  cases 
exists :  In  the  first  the  masonry  may  extend  to  a  con- 
siderable distance  above  the 
level  of  the  water  behind  it, 
the  discharge  being  effected 
by  means  of  a  waste  weir. 
The  water  pressure  against 
its  surface  is  then  in  a  direc- 
tion normal  to  the  horizon- 
tal plane  (Fig.  10).  Such 

Fife.  10.     Direction  of  Pressures  ,         , .    .  ,     ,    . 

on  Dams  pressure  may  be  divided  into 

two  composite  parts,  one  part  of  which  lies  in  a  horizontal 
and  the  other  in  a  vertical  plane.  For  all  practical  purposes 
the  horizontal  component  is  the  only  one  which  need  be 
considered. 

Representing  this  by  J/and  its  height  above  the  base  of 
the  dam  by  h,  the  magnitude  of  these  two  quantities  for  one 
linear  foot  becomes 

M=wh 

where  w  represents  the  weight  of  a  cubic  foot  of  water. 

It  is  obvious  that  the 
horizontal  component 
of  water  pressure  does 
not  depend  on  the  slope 
of  the  dam. 

In  the  more  common 
case  where  the  water  n 

is  discharged  over  the 

top  of  the  dam  (Fig.  n),  let  //,  as  before,  be  the  height 
of  the  dam  and  d  the  depth  of  water  on  the  crest  of 


APPLIED    HYDRAULICS  33 

the  dam.     Then  the  horizontal   pressure  against  its  back 
will  be 

M=  wh  (d  +  $X)  =  J  wh  (h  +  2d). 

Dams  burst  or  fail  from  the  following  causes:  (i)  By 
sliding  ;  (2)  by  rotation  of  the  toe  ;  (3)  by  overturning  ; 
(4)  by  crushing  of  the  material  (if  of  masonry);  (5)  by 
settling  of  the  foundations.  The  first  two  are  the  most 
common  causes  of  failure. 

A  dam  will  slide  when  the  horizontal  pressure  against  its 
surface  equals  or  exceeds  its  frictional  resistance.  Calling 
M  the  horizontal  pressure  against  a  dam,  f  the  coefficient  of 
friction  and  Wa  its  weight,  sliding  occurs  when 


Rotation  of  the  toe  of  a  dam  occurs  when  the  moment  of  M 
equals  the  moment  of  fFwith  respect  to  the  toe.  Or,  fail- 
ure from  this  cause  occurs  when 

Ml  =  Waa, 

in  which  /  and  a  are  the  lever  arms  let  fall  from  the  toe  in 
the  direction  of  M  and  Wa  respectively. 

For  masonry  dams  the  maximum  permissible  pressure 
should  not  exceed  1  5  tons  per  square  foot.  In  some  cases 
it  should  not  exceed  6  tons  per  square  foot. 

A  frequent  cause  of  failure  in  dams  where  the  surplus 
water  is  not  discharged  over  the  crest  is  lack  of  sufficient 
spillway  or  waste  weirs. 

The  most  notable  instance  of  the  failure  of  a  high  dam 
for  hydro-electric  power  development  is  that  of  the  Austin, 
Texas,  municipal  dam.  The  dam  proper  was  1,091  feet  long 
and  68  feet  high.  It  was  built  perfectly  straight  and  con- 


34     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

tained  about  88,000  cubic  yards  of  masonry,  of  which 
70,000  cubic  yards  was  of  rough  rubble  and  18,000  cubic 
yards  of  cut  stone.  The  cost  of  the  dam,  with  the  head- 
gate  masonry,  was  $608,000.  It  was  situated  on  the 
Colorado  River,  two  and  a  half  miles  above  the  city. 

In  a  severe  flood  early  in  April,  1900  (the  highest  in  the 
history  of  the  dam),  about  500  feet  of  the  structure  was 
pushed  bodily  down  stream,  sliding,  apparently,  on  its 
base. 

Storage  Reservoirs.  —  In  regions  —  particularly  the 
Western  States  —  where  the  supply  of  water  from  the 
primary  source  is  not  constant  throughout  the  year, 
means  must  be  resorted  to  for  furnishing  the  deficit  from  a 
secondary  source,  or  reservoir,  during  the  season  of  low 
water. 

.Storage  reservoirs  are  of  two  kinds  —  natural  and  arti- 
ficial. Natural  reservoirs  are  found  principally  in  the  West, 
east  of  the  Rocky  Mountains.  These  natural  basins,  or 
depressions,  collect  the  water  run  off  in  the  wet  season  from 
the  surrounding  watershed,  and  retain  it  in  ponds  until  it 
is  partly  or  wholly  lost  by  evaporation.  Such  natural 
basins  are  frequently  utilized  for  storage  reservoirs  by  con- 
ducting water  into  them  from  adjacent  streams,  and  pro- 
viding them  with  outlets,  by  means  of  which  they  are 
connected  with  the  primary  source  of  supply.  Moreover, 
they  are  frequently  found  at  elevations  sufficiently  high  to 
enable  high  heads  to  be  secured  by  leading  the  pipe  or 
conduit  line  down  the  gradient  into  the  valley  or  canyon, 
wherein  is  located  the  power  plant. 

Artificial  reservoirs  are  generally  formed  by  erecting  a 
dam  across  a  valley  at  a  point  where  the  topography  of  the 
country  is  such  as  to  obviate  any  loss  of  water  into  another 


APPLIED    HYDRAULICS  35 

watershed,  or  by  leakage  from  the  dam.  The  reservoir 
should  also  be  formed  sufficiently  high  up  in  the  valley  to 
permit  the  water  to  flow  freely  to  the  place  of  utilization,  or 
not  infrequently  to  furnish  the  desired  head  of  water  at  this 
point. 

It  is  quite  desirable  that  the  valley  be  narrow  and  the 
surrounding  hills  be  steep  at  the  point  where  the  dam  is 
located,  so  as  to  prevent  both  expensive  construction  and 
shallow  water.  However,  a  basin  or  valley  with  slight 
longitudinal  slope  will  afford  a  given  amount  of  storage  with 
less  height  of  dam  than  one  with  a  precipitous  channel. 

The  location  of  a  reservoir,  or  system  of  reservoirs,  for 
supplying  a  hydraulic  plant  depends  on  the  particular  con- 
ditions which  must  be  met,  such  as  the  quantity  of  water 
which  the  auxiliary  source  of  supply  must  furnish  in  the 
drought  season ;  the  length  of  the  low  season  ;  the  area  of 
the  supplying  watershed,  and  the  quantity  of  water  which 
can  be  impounded  in  the  rainy  season.  ' 

Aside  from  the  water-impounding  area  afforded  by  the 
contour  of  the  country,  the  capacity  of  storage  reservoirs 
depends  on  the  annual  precipitation  and  the  climatic  con- 
ditions in  the  particular  region  ;  the  size  of  the  watershed 
drained,  and  the  losses  from  leakage  and  evaporation.  The 
latter  loss  generally  ranges  from  8  per  cent  to  12  percent 
of  the  consumption.  In  dry,  arid  regions  of  the  West, 
the  loss  by  evaporation  amounts  to  75  per  cent  or  more 
of  the  consumption  per  annum. 

Waste  Weirs  or  Spillways.  —  Waste  weirs  find  appli- 
cation in  discharging  surplus  water  from  reservoirs  or  dams. 
They  are  usually  constructed  in  the  sides  of  a  reservoir, 
and  have  no  end  contractions.  When  a  waste  weir  is 
made  with  a  narrow  crest  and  a  vertical  front,  the  dis- 


36     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

charging  stream  of  water  will  have  air  beneath  it,  and  the 
quantity  of  water  discharged  is,  by  Francis's  formula, 

q  =  3-33  W5T*, 

where  b  represents  the  length  of  the  crest,  and  H  the  head 
measured  at  a  definite  distance  back  of  the  crest.  The 
equation  is  modified  by  a  wide  crest  and  sloping  approach, 
the  discharge  in  such  cases  being  slightly  less.  For  a 
crest  with  inclined  approach  and  about  three  feet  wide,  the 
formula  of  Francis  becomes 


q  =  3.01 

Since  it.  is  extremely  difficult  to  determine  the  exact  dis- 
charge which  is  to  pass  over  a  waste  weir,  the  accurate 
determination  of  its  length  is  unimportant  ;  but  a  large 
factor  of  safety  should  be  allowed  in  order  to  obviate  the 
dangers  from  exceptional  floods. 

When,  as  in  the  case  of  dams,  the  water  flows  over  an 
apron  of  timber  or  masonry,  the  inclination  of  the  material, 
as  well  as  the  inclination  of  the  approach  to  the  crest, 
changes  the  form  of  the  equation,  which  then  becomes 


q  = 

in  which  //"is  the  head  due  to  velocity  of  approach,  and  m 
is  a  constant,  the  value  of   which  ranges  between  2.5   to 

4-3- 

Several  forms  of  waste  weirs  exist:  (i)  Waste  weirs 
excavated  in  natural  soil  at  one  or  both  ends  of  the  dam. 
(This  type  is  not  safe  unless  the  foundation  is  of  rock.) 

(2)  Spillways  channeled  through    some  low  point   in  the 
dividing  ridge  and  the  water  conducted  to  another  valley. 

(3)  A  portion  of  the  dam  (if  of  masonry)  is  designed  as  a 
spillway,  and  is  located  at  about  the  axis  of  the  valley. 


APPLIED    HYDRAULICS  37 

When  spillways  of  the  latter  type  are  used,  their  con, 
struction  should  be  so  substantial  that  the  strains  of  over- 
flow from  floods  will  not  affect  them. 

The  tops  of  spillways  should  also  be  so  designed  as  to 
resist  the  blows  of,  and  pass  over,  logs,  ice,  or  debris, 
brought  down  by  floods. 

Loss  of  Head  in  Pipe  Lines.  — The  principal  sources 
of  loss  which  occur  in  pipe  lines  are  due  to  (i)  Friction  ; 
(2)  contraction  of  the  area ;  (3)  constriction  of  the  orifice  ; 
(4)  curvature. 

The  first  and  principal  loss  is  caused  by  the  resistance  to 
flow  offered  by  the  interior  surface  of  the  pipe.  In  very 
long  pipes  it  becomes  quite  prominent,  so  that  the  dis- 
charge may  be  but  a  small  percentage  of  that  due  to  the 
head. 

The  loss  of  head  by  friction  may  be  ascertained  for  any 
particular  case  by  measurement  of  the  head  //,  the  area  a 
of  the  cross-section  of  the  pipe,  and  the  discharge  q  per 
second. 

Five  approximate  laws  govern  the  friction  loss  in  pipe 
lines:  (i)  The  loss  by  friction  is  proportional  to  the 
length  of  the  pipe.  (2)  It  varies  nearly  as  the  square  of 
the  velocity.  (3)  It  decreases  as  the  diameter  of  the  pipe 
increases.  (4)  It  increases  with  the  roughness  of  the 
inside  surface.  (5)  It  is  independent  of  the  pressure  of 
the  water. 

Or  stated  in  the  form  of  an  equation  : 

/  V* 

fif=-c—    •    — • , 

d  2g 

where  c  is  the  coefficient  of  friction,  /  the  length  of  the 
pipe  in  feet,  d  its  diameter  in  the  same  units,  and  v  the 


38     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

velocity  of  flow.  The  equation  is  but  an  empirical  one 
since  the  theoretical  expression  for  hf  has  not  as  yet  been 
determined. 

The  friction  factor  is  governed  by  the  character  of  the 
interior  surface  of  the  pipe,  diminishing  with  smoothness  of 
surface.  A  value  commonly  employed  is  0.02. 

While  our  knowledge  of  the  internal  frictional  resistances 
of  flowing  water  is  still  in  a  very  unsettled  state,  it  appears 
that  the  energy  transformed  by  friction  into  heat  is  lost  in 
two  ways  :  by  direct  friction  along  the  inside  surface,  and 
by  impact  caused  by  the  varying  motion  of  the  particles  of 
water. 

Loss  of  head,  due  to  the  contraction  of  the  cross-section 
of  a  pipe,  also  causes  a  contraction  of  the  water  stream,  and 
its  tendency  to  expand  to  fill  the  diminished  section  causes 
loss  in  head. 

In  the  case  of  a  gradual  contraction  in  the  cross-section 
of  a  pipe,  which  is  the  more  common  one,  the  loss  in  head 
can  be  determined  for  any  definite  velocity  by  noting  the 
difference  in  height  between  two  pressure  columns,  one  of 
which  is  inserted  just  above  the  point  where  the  cross- 
section  changes,  and  the  other,  slightly  below  the  point 
where  the  contracted  section  commences. 

Having  determined  the  values  for  the  velocities  v,  and 
z>2>  and  the  heads  k,  and  h^  in  the  respective  cross-sections, 
the  loss  in  head,  occasioned  by  a  contraction  of  cross- 
section,  becomes 


If  there  is  no  subsequent  increase  of  cross-section,  the  loss 
of  head  from  this  cause  is  not  appreciable,  since  it  is  due  to 
loss  of  velocity  caused  by  abrupt  expansion. 


APPLIED    HYDRAULICS  39 

Loss  of  head  in  a  pipe  line  may  also  be  caused  by  a  sud- 
den constriction  of  the  orifice  of  the  pipe.  It  is  explained 
by  the  fact  that  the  particles  of  water,  as  they  approach 
the  orifice,  move  in  converging  directions  ;  hence  such 
contraction  of  the  stream  causes  only  the  inner  corner  of 
the  orifice  to  be  touched  by  the  water  in  its  outward  pas- 
sage. 

When  a  pipe  line  is  laid  on  a  curve  the  water  flow  is 
changed  in  direction,  which  causes  an  increase  of  pressure 
in  the  direction  of  the  radius  of  the  curve  and  away  from 
its  center.  The  increase  of  pressure  sets  up  eddying 
movements  in  the  water,  causing  impacts  against  the  wall 
of  the  pipe.  Such  impacts  dissipate  some  of  the  energy  of 
the  head  by  transforming  it  into  heat.  It  is  obvious  that 
the  loss  of  head  hc,  caused  by  a  curve  in  a  pipe  line,  in- 
creases with  its  length.  It  is  also  larger  for  small  pipes 
than  for  large  ones. 

The  loss  of  head,  caused  by  a  curve  in  a  pipe  line,  is 
expressed  by  the  following  equation, 


in  which  fc  is  a  number  termed  the  curve  factor,  the  value 
of  which  depends  upon  the  ratio  of  the  radius  of  the  pipe 
to  its  diameter  ;  /  is  the  length  of  the  curve  ;  d  the  diam- 
eter of  the  pipe,  and  v  the  mean  velocity  of  flow.  Repre- 
senting by  R  the  radius  of  the  circle  in  which  the  center 

r> 

line  of  the  pipe  is  laid,  as  the  ratio  —  decreases,  the  value 

d    • 

of  fc  increases. 

Owing  to  a  lack  of  sufficient  experimental  data  to  deter- 
mine accurate  values  for  the  curve  factor  fc,  the  equation 


40     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

can  only  be  considered  as  a  rough  guide.  For  cast  iron 
pipe,  Messrs.  Hubbell  and  Frenkell  determined  the  follow- 
ing values  of  the  curve  factor  for  3O-inch  pipe  laid  with  a 
curve  of  90  degrees  : 


—  =    24          16         10  6  4  2.4 

a 

f-c  =  0.036     0.037     0.047     0.060     0.062     0.072. 

When  there  are  several  bends  or  curves  in  a  pipe  line,  the 
value   of  fc  —  is  computed  for  each  curve  ;  and  the  sum  of 

these  values  is  taken  in  order  to  find  the  total  loss  of  head 
due  to  the  curvatures. 

The  equation  then  becomes 


in  which  k  represents  the  sum  of  these  values  for  all  the 
curves. 

The  loss  in  head  caused  by  curves  in  a  pipe  or  flume  line 
is  generally  small  compared  with  that  lost  in  friction,  as 
the  curves  are  made  as  few  and  as  slight  as  possible. 

Mean  Velocity  of  Flow  in  Pipes.  —  Assuming  that  the 
pipe  is  running  full,  the  formula  for  mean  velocity  of 
flow  can  be  deduced  from  the  factors  which  have  been 

9 

V 

thus   far    stated.     Let   Ji   be   the   maximum    head,  —  the 

v2 
effective  velocity  head  of  the  issuing  stream,  and  h  -- 

the  lost  head.  The  lost  head  is  equal  to  the  sum  of  its 
component  parts,  which  may  be  called  //'  -f  hj  -f-  hc. 


APPLIED    HYDRAULICS 


Loss  of   Head   in    Pipe   by   Friction 

The  following  tables  show  the  loss  of  head  by  friction  in  each  100  feet  in  length  of  different- 
diameters  of  pipe,  when  discharging  the  following  quantities  of  water  per  minute  : 

INSIDE  DIAMETER  OF  PIPE   IN  INCHES. 


13 

14 

15 

16 

18 

20 

Vel. 

Loss   of1   Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

in  ft. 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

per 

per 

in 

per 

in 

per 

in 

per 

in 

per 

in 

per 

sec. 

feet. 

min. 

feet. 

min. 

feet. 

feet. 

min. 

feet. 

min. 

feet. 

mm. 

2.0 

.183 

110. 

.169 

128. 

.158 

147. 

147 

167. 

.132 

212. 

.119 

262. 

2.2 

.216' 

121. 

.200 

141. 

.187 

162. 

175 

184. 

.156 

233.- 

.140 

288. 

2.4 

.252 

133. 

.234 

154. 

.2tf 

176.. 

.205 

201. 

.182 

254. 

.164 

314. 

2.6 

.290 

144. 

.270 

167. 

.252 

191. 

.236 

218. 

.210 

275 

.189 

340. 

2.8 

.332 

156. 

.308 

179 

.288 

206. 

.270 

234. 

.240 

297. 

.216 

366. 

3.0 

.375 

166, 

.349 

192. 

.325 

221. 

.306 

251. 

.271 

318. 

.245 

393. 

3.2 

.422 

177. 

.392 

205. 

.366 

235. 

.343 

268. 

.305 

339. 

.275 

419 

3.4 

.471 

188. 

.438 

218. 

.408 

250. 

.383 

284. 

.339 

360. 

.306 

445. 

3.6 

.522 

199 

.485 

231. 

.452 

265. 

.425 

301. 

.377 

382- 

,339 

471. 

3.8 

.576 

210. 

.535 

243. 

.499 

280.' 

.468 

318. 

.416 

403, 

.374 

497. 

4.0 

.632 

221. 

.587 

256. 

.548 

294. 

.513 

335. 

.456 

424. 

.410 

523. 

4.2 

.691 

232. 

.641 

269. 

.598 

309. 

.561 

352. 

.499 

445. 

.449 

550. 

4.4 

.751 

243. 

.698 

282. 

.651 

324. 

.611 

368. 

.542 

466. 

.488 

576. 

4.6 

.815 

254. 

.757 

295. 

.707 

339. 

.662 

385. 

.588 

488. 

.529 

602. 

4.8 

.881 

265. 

.818 

308. 

.763 

353. 

.715 

402. 

.636 

509 

.572 

628. 

5.0 

.949 

276. 

.881 

321. 

.822 

368. 

.770 

419. 

.685 

530. 

.617 

654. 

5.2 

1.020 

287. 

.947 

333. 

.883 

383. 

.828 

435. 

.736 

551. 

.662 

680. 

5.4 

1.092 

298. 

1.014 

346. 

;947 

397. 

.888 

452. 

.788 

572. 

.710 

707. 

5.6 

1.167 

309. 

1.083 

359. 

1.011 

412. 

.949 

469. 

.843 

594. 

.758 

733. 

5.8 

1.245 

321. 

1.155 

372. 

1.078 

427. 

1.011 

486. 

.899 

615. 

.809 

759. 

60 

1.325 

332. 

1.229 

385. 

1.148 

442. 

1.076 

502. 

.957 

636 

.861 

785. 

7.0 

1.75 

387. 

1.630 

449. 

'1.520 

515. 

1.430 

586. 

1.270 

742. 

1.143 

9.16. 

INSIDE    DIAMETER    OF    PIPE    IN    INCHES. 


22 

24 

26 

23 

30 

36 

Vel. 

Loss  o 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  of 

Cubic 

Loss  o( 

Cubic 

In  ft. 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

head 

feet 

per 

per 

in 

per 

in 

per 

in 

per 

in 

per 

in 

per 

.sec. 

feet. 

min. 

feet. 

min. 

feet. 

feet. 

min. 

feet. 

min. 

feet 

min. 

2.0 

.108 

316. 

.098 

377. 

.091 

442. 

084 

513. 

.079 

589: 

.066 

'848. 

2.2 

.127 

348. 

.116 

414. 

.108 

486. 

.099 

564 

.093 

648. 

.078 

933. 

2.4 

.149 

380. 

.136 

452. 

.126 

531. 

.116 

616. 

.109 

707. 

.091 

1018. 

2.6 

.171 

412. 

.157 

490. 

.145 

575. 

.134 

667. 

.126 

766. 

.104 

1100. 

2.8 

.195 

443 

.180 

528. 

.165 

619. 

.153 

718. 

.144 

824. 

.119 

1188. 

30 

.222 

475. 

.204 

565. 

.188 

663. 

.174 

770. 

.163 

883. 

.135 

1273. 

8.2 

.249 

507. 

.229 

603. 

.211 

708. 

.195 

821. 

.182 

942. 

.152 

1357. 

3.4 

.278 

538 

.255 

641. 

.235 

752. 

.218 

872. 

.204 

1001. 

.169 

1442. 

3.6 

.308 

570. 

.283 

678. 

.261 

796. 

.242 

923. 

.226 

1060. 

.188 

1527. 

3.8 

.340 

601. 

.312 

716. 

.288 

840. 

.267 

974. 

.249 

1119. 

.207 

1612. 

4.0 

.373 

633. 

.342 

754. 

.315 

885. 

.293 

1026. 

.273 

1178. 

.228 

1697. 

42 

.408 

665. 

.374 

791. 

.345 

929 

.320 

1077. 

.299 

1237. 

.249 

1782. 

4.4 

.444 

697. 

.407 

829. 

.375 

973. 

.348 

1129. 

.325 

1296. 

.271 

1866. 

4.6 

.482 

728. 

.441 

867. 

.407 

1017 

.378 

1180. 

.353 

1355. 

.294 

1951. 

48 

.521 

760. 

.476 

905. 

.440 

1062. 

.409 

1231. 

.381 

1414. 

.318 

2036. 

6.0 

.561 

792. 

.513 

942. 

.474 

1106. 

.440 

1283. 

.411 

1472. 

.342 

2121. 

5.2 

.602 

823. 

.552 

980. 

.510 

1150. 

.473 

1334. 

.441 

1531. 

.368 

2206. 

54 

.645 

855. 

.591 

1018. 

.546 

1194. 

.507 

1385. 

.473 

1590. 

.394 

2291. 

56 

.690 

887. 

.632 

1055. 

.533 

1239. 

.542 

1437. 

.506 

1649. 

.421 

2376. 

5.8 

.735 

918. 

.674 

1093. 

.622 

1283. 

.578 

1488. 

.540 

1708. 

.450 

2460. 

6.0 

782 

950. 

.717 

1131. 

.662 

1327. 

.615 

1539. 

.574 

1767. 

.479 

2545. 

7.0 

1.040 

1109. 

.953 

1319. 

.879 

1548. 

.817 

1796. 

.762 

2061. 

.636 

2968. 

The  following  formula,  deduced  by  Wm.  Cox,  gives  practically  the  same  results  as  the 
above  table  and  will  be  found  useful  in  many  instances.  F  =  -^-^  (4  V2  +  5  V-2).  Where 
F  —  friction  head,  L  —  length  of  pipe  in  feet;  D  —  diameter  of  pipe  in  inches;  V  —  velocity 
in  feet  per  second. 


Table  I 


42     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Substituting  the  values  of  //,  hp  and  hc,  from  the  pre- 
vious paragraphs, 

1?  V*  I  7?  tf 

h  = h  m h  c—   . t-  «— , 

2^  2g  (t          2g  2g 

V2 

where  m  —  is  the  loss  of  head  at  the  entrance  (negligible 

& 

72  2 

for  long  pipes)  \c-,*  — ,  the  loss  by  friction,  and  n  — ,  the 
d     2g  2g 

loss  due  to  curvature. 

Solving  for  v,  the  equation  becomes 


-v/ 


i  +  m  +  C-,  +  // 
a 


which    is  applicable    satisfactorily    to   pipes    of    moderate 
length. 

Determination  of  Discharge  from  Pipes.  —  The  dis- 
charge per  second  from  any  pipe  of  a  given  diameter  is 
found  by  multiplying  the  area  of  its  cross-section  by  the 
velocity  of  discharge,  which,  stated  as  a  formula,  is 


Determination  of  the  Diameter  of  Pipe  to  Discharge  a 
Given  Quantity  of  Water.  —  Let  d  represent  the  diameter, 
/  the  required  length  of  the  pipe  line,  q  the  quantity  of 
water  to  be  discharged,  h  the  head,  and  f  the  coefficient 
of  friction  (0.02). 

Neglecting  the  influence  of  curvature,  an  equation  for 
diameter  is 


d  =  o.479 
in  which  the  values  of  //,  /,  and  d  are  taken  in  feet,  and  that 


APPLIED    HYDRAULICS  43 

of  q  in  cubic  feet  per  second.  In  applying  this  formula 
two  computations  are  generally  made.  In  the  first  calcu- 
lation, d  in  the  right-hand  side  is  disregarded  and  a  rough 
value  for  the  diameter  is  calculated.  Then  determining 
the  velocity  from  the  equation 


the  friction  coefficient  for  this  velocity  is  looked  up  in  a 
table  of  coefficients.  A  second  calculation  of  d  is  then 
made,  using  in  the  right-hand  side  of  the  equation  the 
rough  value  of  d  first  derived. 

To  arrive  at  the  value  of  d  with  a  fair  degree  of  accu- 
racy, several  computations  are  generally  made,  using  each 
time  the  approximate  value  of  d  obtained  by  the  preceding 
computation. 

Long  Pipes.  —  A  pipe  is  said  to  be  long  when  its  length 
is  approximately  4,000  times  its  diameter,  or  more.  In 
the  West,  particularly  in  California,  the  pipe  or  flume  lines 
which  conduct  the  impounded  water  to  the  hydraulic 
machines  range  in  length  from  a  few  hundred  feet  up  to 
seven  miles  or  more,  and  it  is  with  this  class  of  pipes  that 
we  are  principally  concerned. 

In  long  pipes  the  friction  loss  predominates,  the  velocity 
head  being  usually  small.  The  expression  for  velocity, 
when  a  long  pipe  is  running  full,  is 


in  which   the   letters   have   the    significance   assigned   in 
previous  paragraphs. 


44     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  discharge  per  second  through  a  long  pipe  is  given 
by  the  expression 

*  *  f**k 

6-3°V^r 

Maximum    Energy    Transmitted    by   a   Water  Pipe.  — 

Let  Q  =  total  cubic  feet  of  water. 
D  =  diameter  of  the  pipe. 
h  =  total  head. 
/  =  length. 

The  relation  between  these  quantities  becomes 


A  cubic  foot  of  water  falling  through  a  distance  of  one 
foot  develops 

62.5  x  60 

—  =  0.1135  horse-power. 
33,000 

Then  H.  P.  =0.1135  Q  H> 

where  H  equals  the  distance  of  fall  in  feet  and  Q  =  quan- 
tity of  water  in  cubic  feet  per  second.  Hence  if  hf  is  the 
loss  of  head  due  to  friction,  the  horse-power  delivered  at 
any  distance  L  feet  away  is 

H.  P.  =  0.1135  Q  (H~  hf)- 
By  substituting  the  value  of  Q  the  relation  becomes 


H.  P.  =  0.1135  X  38.5  •  D\     (H~  fa 
Calling   the  value  of  hf  equal  to  kH  (where  k  equals 


APPLIED    HYDRAULICS  45 

the  sum  of  all  the  curve  factors)  we  get  by  substituting  and 
reducing 


H.  P.  = 


The  first  formula  gives  the  horse-power  that  can  be 
transmitted  for  any  definite  fraction  of  the  head  lost  in 
friction  ;  and  the  second,  the  length  of  pipe  which  will 
transmit  a  given  amount  of  power  with  a  given  loss. 

Loss  of  head  is  proportional  to  F2  and  loss  of  power  to 
V,  hence  the  maximum  power  is  transmitted  when  one- 
third  of  the  head  is  dissipated  in  friction. 

Mean  Velocity  of  Flow  in  Canals  and  Conduits.  —  The 
general  empirical  formula  of  Chezy  for  the  mean  velocity 
of  flow  in  streams  is  also  applicable  to  conduits  and 
canals,  and,  with  some  modifications,  to  all  forms  of  chan- 
nels. For  a  circular  conduit  running  full  or  half  full,  the 
hydraulic  radius  r  —  \d  ;  hence  the  mean  velocity  is 


•v  =  c  \rs  =  c  . 

where  c  is  the  friction  coefficient,  the  value  of  which 
depends  upon  the  roughness  of  the  conduit  and  its  curva- 
ture, and  s  is  the  slope. 

The  discharge  from  the  same  kind  of  channel  is  then 
given  by  the  equation 

q  =  av  =  c  .  \a  v5jr, 

in  which  a  is  either  one-half  of  the  area  of  the  cross- 
section,  or  the  entire  circular  cross-section. 


46     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

For  a  rectangular  conduit,  the  velocity  and  discharge  are 
given  by  the  equations 


v  =  c  *\frs     and     q  =  av  =  c  •  a  *Jrs, 

the  values  of  c  being  taken  from  a  table  of  coefficients 
for  circular  conduits. 

In  case  the  depth  of  water  is  greater  or  less  than  one- 
half  the  diameter  of  the  pipe,  the  value  of  c  increases  with 
r.  It  also  increases  greatly  with  the  degree  of  roughness. 

The  empirical  formula  of  Kutter  (derived  from  the 
experiments  conducted  by  Ganguillet  and  Kutter  in  1869) 
is  now  universally  employed  for  determining  the  value  of  c 
in  the  Chezy  formula,  since  it  is  applicable  to  all  kinds  of 
surfaces.  In  fact,  it  may  be  said  in  general,  that  no 
design  for  channels  is  now  made  without  its  employment 
in  the  preliminary  investigations.  The  formula  of  Kutter 
for  c  is 

i.8n   , 
c  =  -  --  h  41.65  +  0*00 


n    I 
_(4I.6s 


where  r  is  expressed  in  feet,  and  v  in  feet  per  second ;  n  is 
an  abstract  number  of  a  value  depending  upon  the  charac- 
ter of  the  surface. 

In  Kutter's  formula  the  value  of  c  is  expressed  in  terms 
of  the  hydraulic  radius  r,  slope  s,  and  the  degree  of  rough- 
ness of  surface. 

The  Contruction  of  Flumes. —  Flumes  are  frequently 
employed  for  conveying  water  to  hydro-electric  plants,  but 
are  not  considered  as  economical  as  pipe  systems  or  con- 
duits, since  the  loss  in  leakage  is  greater;  and  they  are 


APPLIED    HYDRAULICS  47 

also  more  liable  to  damage  or  destruction  from  snow- 
storms, wind,  and  decay.  In  mountainous  regions,  how- 
ever, where  timber  is  abundant,  and  the  cost  of  transport- 
ing the  pipe  system  prohibitive,  their  use  may  be  more 
advantageous  than  other  forms  of  water-conducting  sys- 
tems. A  flume  can  be  made  much  smaller  than  a  canal 
on  account  of  the  high  permissible  velocity  of  water  in  it, 
which  is  usually  about  6  or  8  feet  per  second.  Flumes  also 
offer  much  less  resistance  to  the  flow  of  water  than  canals, 
which  give  a  smaller  loss  of  head  for  the  same  capacity. 

Flumes  are  generally  constructed  in  rectangular  form  of 
durable  timber,  and  are  supported  either  on  trestles,  or 
stone  or  concrete  blocks.  When  a  flume  system  is  sup- 
ported on  level  benches,  cut  in  the  hillside  or  soil,  the 
flume  is  termed  a  bench  flume.  Bench  flumes  are  sup- 
ported on  concrete  brick  or  solid  stone.  In  crossing  a 
rough  section  of  country,  or  a  valley  or  divide,  flumes  are 
supported  on  trestles. 

The  timber  used 'in  the  construction  of  flumes  should  be 
of  a  variety  which  does  not  easily  decay,  and  which  is  also 
plentiful  in  the  neighborhood.  When  a  flume  line  is  laid 
near  the  base  of  a  hillside  or  mountain,  the  bed  on  which 
it  rests  should  be  excavated  in  the  side  of  the  elevation, 
and  the  flume  laid  very  close  to  the  bank,  as  a  precaution 
against  damage  from  snow  or  wind  storms.  In  exposed 
places,  flumes  are  covered  with  planks  and  timber  from 
two  to  six  inches  in  thickness,  as  a  protection  against  roll- 
ing bowlders  and  landslides. 

In  California,  where  flumes  are  extensively  used  as  water- 
conducting  systems  for  hydro-electric  plants,  the  flume 
boxes  are  generally  constructed  of  clear,  surfaced  redwood, 
placed  in  position  longitudinally  to  the  flow  of  water.  The 


48     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


trestle  caps,  stringers,  and  yokes  are  usually  made  of  Ore- 
gon pine. 

Fig.  12  shows  a  type  of  California  flume  constructed 
of  the  materials  as  stated  above. 

Flumes  are  braced  at  intervals  of  several  feet  by  diag- 
onal scantlings  nailed  to  horizontal  timbers  or  sills,  fas- 
tened to  the  bottom.  The  construction  employed  when  the 

loss  in  leakage  is  desired 
,wire  Naiis  to  be  kept  as  small   as 

possible,  consists  of  a 
double  thickness  of 
planking,  the  inner  one 
being  sometimes  coated 
with  tar  or  asphaltum  to 
prevent  any  seepage  of 
water,  and  also  to  pro- 
long its  life.  The  length 
of  life  of  a  flume  is 


f 


•9'-  9 


If  fc  I  4  Batten 


^Boxes  12  Ft.Long 


\\  Bottom  &  Sides 
*XA  Cut  Nail? 


34  to  Lb. 


l^Gtln. 

"'SO  Nails  4"  Long 
about  35  to  Lb. 


Two  SetB  of  Three 
Intermediate  Poets 


Fig.  12.    Type  of  Flume  used  in  Some 
California  Plants 


greatly  prolonged  by 
creosoting  the  timber, 
but  the  construction  is 
rendered  much  more 
expensive  thereby. 
A  type  of  flume  used  principally  on  the  Pacific  coast  is 
known  as  the  stave  and  binder  flume.  In  this  type  the 
bottom  is  constructed  like  the  lower  half  of  wood  stave 
pipe,  but  vertical  sides  are  used  instead  of  the  closed  top. 
A  binding  rod  is  passed  around  the  flume,  its  ends  passing 
through  the  two  ends  of  a  cross-head,  and  provided  with 
nuts  by  means  of  which  the  staves  are  forced  together. 
Flumes  of  this  shape  are  supported  on  T-shaped  frames 
made  of  T-iron,  and  resting  on  wooden  bolsters,  spaced 


UNIVERSITY 

or 


HYDRAULICS 


49 


about  8  feet  apart ;  each  frame  resting  on  concrete  blocks. 
Trestles  for  supporting  flume  lines  are  made  of  either 
wood  or  steel,  with  footings  constructed  of  a  cement  con- 


Fig.  13.    Flume  Supported  on  Trestle 

crete.  Fig.  1 3  shows  a  flume  line  carried  on  a  wooden 
trestle. 

Waste  flumes  are  designed  to  carry  away  the  overflow 
from  forebays,  and  are  similar  in  design  to  conducting 
flumes. 

When  a  flume  or  water-conducting  channel  runs  through 
a  forest,  means  must  be  adopted  to  prevent  leaves  and 
twigs  which  fall  in  the  water  from  entering  the  connecting 
pipe  line  or  penstock.  Figs.  14  and  15  illustrate  a  device 
employed  in  the  flume  line  of  the  Mill  Creek  Plant  of  the 
California  Edison  Company,  to  free  the  water  of  such 


50     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

matter  before  it  reaches  the  connecting  pipe  line.  It  com- 
prises an  endless  wire  screen,  wound  over  two  drums,  the 
lower  end  of  the  screen  being  immersed  in  the  water,  thus 
catching  and  removing  the  floating  matter  from  the  water, 
and  depositing  it  in  a  mass  underneath  the  upper  end. 
Movement  of  the  screen  drum  is  effected  by  means  of  a 


Fig.  14.    Device  for  Removing  Leaves  and  Twigs  from  Flume  Lines 

sprocket  chain  actuated  by  an  undershot  wheel,  which  is 
operated  by  the  current  in  the  flume. 

Precautions  are  also  adopted  to  prevent  the  sand  which 
enters  the  flume  line  from  the  supplying  stream,  from 
getting,  into  the  connecting  line,  where  it  would  quickly 
abrade  the  metal  and  cause  serious  damage  to  the  nozzles 
and  buckets  of  the  wheel, 


APPLIED    HYDRAULICS  5  I 

Circumferential  Pressure  in  Pipes. — 

Let  /  =  intensity  of  strain, 

r  =  radius  of  pipe, 
p  =  pressure-head, 
/  =  thickness  of  shell. 

Then  /  =  ^T 

For  stresses  in  riveted  steel  pipe  : 

Let  /  =  intensity  of  strain, 

e  ==  modulus  of  elasticity, 
/  =  change  of  temperature, 
k  —  coefficient  of  expansion. 

Then  i=etk. 

The  Construction  of  Pipe  Lines.  —  The  method  of  con- 
veying water  to  hydraulic  machines  by  means  of  pipe  lines 
has  become  almost  universal  practice  on  the  Pacific  coast, 
and  in  mountainous  sections  of  the  West.  The  material 
used  in  the  construction  of  pipe  lines  is  either  wood,  cast 
iron,  wrought  iron,  or  steel,  the  latter  being  generally  used 
in  the  riveted  form. 

The  use  of  wood  stave  pipe  as  a  conveying  medium  for 
water  is  quite  general  in  some  sections  of  the  West.  It  is 
constructed  of  redwood,  fir,  cypress,  pine,  or  other  durable 
woods  with  wooden  tongue-butt  joints,  the  sections  being 
bound  with  steel  bands,  and  held  together  with  clips  or 
shoes  made  of  cast  iron.  The  pressure  which  a  wooden 
stave  pipe  can  safely  withstand  depends  upon  the  hardness 
of  the  saturated  wood — a  working  head  of  200  feet 
having  been  shown  by  experience  to  be  a  safe  practical 
limit  in  the  case  of  redwood  and  Douglass  fir. 


52     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Among  the  advantages  claimed  for  wooden  stave  pipe 
are:  (i)  Greater  discharging  capacity  than  metal  pipe  of 
the  same  diameter,  due  to  the  fact  that  the  friction  factor 
does  not  increase  with  age  —  i.e.,  they  do  not  become 
rougher  with  age.  (2)  The  materials  for  constructing  a 
stave  pipe  can  be  easily  transported  to  the  region  through 


Fig.  15.     Undershot  Wheel  which  Actuates  Device  Shown  in  Fig.  14 

which  a  pipe  line  must  be  laid,  and  the  pipe  system  con- 
structed on  the  site.  This  is  an  important  advantage  when 
the  water-conducting  medium  traverses  a  rough  and  moun- 
tainous country  where  it  would  be  very  difficult  or  impos- 
sible to  transport  heavy  metal  pipe.  (3)  It  is  cheaper  than 
metal  pipe.  The  cost  of  a  30  inch  redwood  pipe  laid  and 
buried  was  $3.90  per  foot  for  200  feet  head.  * 

*  Adams,  Transactions  American  Society  Civil  Engineers,  1898,  p.  676. 


APPLIED    HYDRAULICS 


53 


The  disadvantages  of  stave  pipe  are  :  (i)  It  is  shorter 
lived  than  metal  pipe.  It  is  manifest  that  changes  of 
temperature  and  wind  will  cause  a  steady  movement  back 
and  forth  of  the  limit  of  saturation  within  the  staves,  thus 
leaving  the  outer  skin  of  the  wood  in  a  condition  which  in- 
vites decay.  Adams  claims,  however,  that  there  are  some 
stave  pipe  lines  in  New  England  that  are  constructed  of 
pine  and  have  lasted  from  20  to  40  years.  Evidently, 
redwood  pipe  lines  should  last  much  longer.  (2)  It  is 


Fig.  16.     Construction  of  Stave.  Pipe  Line 

subject  to  attack  from  insects,  rodents,  etc.  (3)  Evapora- 
tion losses  from  wood  pipe  are  considerable. 

To  prevent  evaporation  losses  it  has  been  proposed  to 
put  a  protective  coating  of  asphalt  or  paint  on  the  outside 
of  the  pipe. 

Fig.  1 6  shows  the  construction  of  a  Wheeler  continuous 
stive  pipe,  made  by  the  National  Wood  Pipe  Co.,  of  Los 


54     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Angeles,  and  Fig.  17  shows  a  completed  pipe  line.  Stave 
pipe  is  used  in  sizes  ranging  from  a  few  inches  up  to  10 
feet  in  diameter. 

When  iron  pipe  is  used,  cast  iron  is  preferable  to 
wrought  iron,  since  it  rusts  materially  less  than  wrought 
iron,  and  its  life  is  practically  unlimited.  It  is  also  non- 


Fig.  17.    Completed  Wooden  Pipe  Line 

collapsible  and  capable  of  withstanding  as  high  hydrostatic 
pressures  as  wrought  iron. 

In  some  Western  transmission  practice  the  pipe  lines 
are  constructed  of  steel  or  wrought  iron  in  one  part  of 
their  length,  and  cast  iron  in  the  other ;  and  are  graduated 
in  thickness,  being  of  heaviest  metal  near  the  receivers. 

The  joints  used  on  continuous  metal  pipe  are  usually  of 
the  flange  type,  the  sections  being  bolted  together.  Fig.  i  Sa 
shows  a  type  of  joint  used  on  the  cast  iron  pipe  line  of  a 


APPLIED    HYDRAULICS 


55 


Fig.  i8a.    A  Type  of  Joint  for  High-head 
Pipe  Lines 


California  transmission  company.  A  groove  extends  round 
the  flange,  into  which  is  forced  a  circular  rubber  gasket  of 
a  slightly  smaller  diameter  than  the  groove  in  the  flange. 
It  is  placed  in  the 
groove,  and  when  the 
rivets  are  inserted  and 
the  flanges  drawn  to- 
gether, the  sections  of 
pipe  are  united  metal 
to  metal.  Water  press- 
ure tends  to  force  the  gasket  more  firmly  into  the  recess 
of  the  flange  and  insures  absolute  water  tightness. 

Iron  pipe  for  conveying  water  to  hydro-electric  plants  is 
rarely  used  in  sizes  larger  than  3  or  4  feet  in  diameter. 

Riveted  pipe  is  more  widely  used  for  a  water-conducting 
medium  than  any  other  kind  of  metal  pipe.  It  is  made 
from  iron  or  sheet  steel  plates  of  the  thickness  required  to 
withstand  the  pressure,  these  being  rolled  to  the  desired 
diameter.  The  plates  or  sheets  are  held  together  by  a 
double  or  triple  row  of  rivets  along  the  longitudinal  seam, 
and  a  single  row  of  rivets  along  the  circular  seams.  As  a 
protection  against  corrosion  and  in  order  to  decrease  the 
frictional  resistance,  each  section  of  pipe  is  immersed  in  a 
vat  of  hot  asphaltum,  which  gives  it  a  smooth  finish  on  the 
interior. 

The  sections  of  riveted  pipe  are  joined  together  either 
by  means  of  slip  joints,  if  the  head  of  water  on  the  line 
does  not  exceed  350  feet;  or  by  means  of  collar  and  sleeve 
joints,  when  the  head  is  not  much  over  750  feet ;  or  by 
flanged  joints,  when  the  head  is  considerably  above  750 
feet. 

On  most  riveted  pipe,  joints  are  made  by  means  of  a 


56     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


single  row  of  rivets  commonly  called  "  round  seams."  In 
this  style  of  riveting,  holes  are  accurately  punched  by  a 
multiple  punching  machine,  and  the  joints  of  the  sections 
riveted  with  cold  rivets  on  light  gauges,  and  hot  rivets  on 
the  heavier  gauges.  The  pipe  is  then  chipped  and  caulked 
to  insure  a  water-tight  joint,  metal  to  metal,  around  the 
joint.  At  points  where  the  lap  in  the  joint  occurs,  the 


Fig.  i8b  Fig.  i8c 

Size  and  Spacing  of  Rivets  on  Pipe  Lines 

metal  of  the  overlapping  joint  is  likewise  chipped  and 
caulked.  Finally,  the  inside  and  outside  of  the  joint  are 
painted  with  asphaltum  as  a  protection  against  corrosion  by 
the  action  of  water  and  chemicals  in  the  soil. 

Pipe  ranging  from  24  inches  in  diameter  upward  is  gen- 
erally continuous-riveted,  and  varies  in  thickness  from  No. 
14  to  oooo  B.  W.  G.  Lap  welded  pipe  for  heavier  gauges 
is  also  quite  common. 

On   lighter   gauge  pipes  "bump"  joints  are  generally 


APPLIED    HYDRAULICS 


57 


used.  These  are  constructed  by  expanding  one  end  of  a 
section  enough  to  permit  the  other  near  end  of  the  next  sec- 
tion to  enter  it.  Then  holes  are  punched  through  both  the 
sections  of  pipe,  at  the  ends  to  be  joined  together,  and  the 
riveting  done  by  means  of  hot  rivets  in  a  similar  manner 
to  that  employed  on  round  seams. 

Usually,  on  very  light  gauges  of  pipe  of  the  bump  joint 


IXB.W.%.  SHEET. 

Fig.  i8d  Fig.  i8e 

Size  and  Spacing  of  Rivets  on  Pipe  Lines 

type,  a  single  row  of  rivets  is  used  on  the  joint.  On  pipes 
of  from  one-half  to  three-fourths  inch  diameter,  double 
rivets  are  generally  used,  and  the  rivets  staggered  as  on 
straight  seams  on  riveted  pipe.  Figs.  i8£,  iSc,  i8d,  and 
1 8^,  show  the  size  and  spacing  of  rivets  used  in  many 
Western  pipe  lines. 

Figs.  19,  20,  and  21  show  the  three  methods  of  connec- 
tion employed  on  riveted  pipe,  and  also  illustrate  riveted 
steel  pipe  made  by  the  Pelton  Wheel  Company.  Riveted 


58     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


section  pipe  has  been   satisfactorily  employed  to  convey 
water  under  heads  up  to  2,000  feet. 

The  material  used  in  some  pipe  lines  is  open  hearth,  box- 
annealed  steel  of  a  tensile  strength,  ranging  from  40,000 
to  6o,OOO  pounds  per  square  inch,  and  with  riveted  joints. 
The  preference  for  steel  over  iron  is  to  some  extent  a 


SLIP      JOINT 


SUP        JOINT         PIPE 


LEAD     JOINT 


.COLLAR  AND  SLEEVE   LEAD  JOINT 


...    FLANGED   JOINT 


SECTIONS    SHOWiNG    GASKETS 


Figs.  19,  20,  21.     Methods  of  Connecting  Riveted  Pipe 

matter  of  cost.  Pipes  are  calculated  to  resist  a  certain 
pressure,  and  the  greater  tensile  strength  of  steel  is 
an  important  factor  ;  in  order  to  resist  the  same  pres- 
sure an  iron  pipe  of  much  greater  weight  would  be 
required. 

On  the  other  hand,  steel  pipe  is  much  more  liable  to  be 
damaged  by  electrolytic  action  when  laid  on  alkali  soils. 
Under  such  conditions  iron  and  carbon  form  the  two  ele- 


APPLIED    HYDRAULICS 


59 


ments,  differing  in  the  electrochemical  series,  while  alkali  is 
the  electrolyte. 

With  iron  pipe  very  little  electrolytic  action  ensues, 
since  iron  contains  very  little  carbon. 

Pipe  lines  for  conveying  water  to  hydro-electric  plants 
are  generally  laid  on  the  surface  of  the  ground,  and  when 
the  gradient  is  steep  they 
are  securely  anchored  by 
embedding  them  in  cement 
blocks  spaced  10  or  15  feet 
apart.  Fig.  22  shows  the 
pipe  line  and  method  of 
anchoring  adopted  by  the 
Bay  Counties  Power  Com- 
pany of  California. 

In  some  cases  pipe    sys- 
tems   are    laid    in    trenches 
from  3  to  6  feet  deep  and 
back-filled    with    earth    and 
rock.       At     various    points 
along  the  line  heavy  anchors 
of   concrete  are  placed,  ex- 
tending  all   around   the    pipe.       These    anchorages    are 
generally  dovetailed  into  the   solid  rock  in  the  sides  and 
bottom  of  the  trench,  and  hold  the  pipe  rigidly. 

All  curves  on  pipe  lines  should  be  made  with  a  long 
radius  to  reduce  the  loss  of  head.  At  points  near  the 
receiver,  and  where  inverted  siphons  are  used,  blow-offs, 
air  valves,  or  other  safety  devices  should  be  installed  in 
order  to  prevent  accidents  from  bubbles,  water  hammer, 
and  vacuum. 

A  standpipe  for  the  escape  of  air  bubbles  is  sometimes 


Fig.  22.     Method  of  Anchoring  Pipe 
Lines  on  Steep  Grades 


6O     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


Table    of   Riveted    Hydraulic    Pipe 

Showing  price  and  weight,  with  safe  head  for  various  sizes  of  double  riveted  pipe. 
(  Revised  ) 


Diameter  of  pipe  (n  || 
inches 

Thickness  of  material 
U.  S.  standard  gauge 

Equivalent  thickness 
in  inches. 

Head  itrfeet  pipe  will 
safely  stand. 

1 
Weight  per  lineal  foot 
in  pounds. 

% 
8 

*c 

a, 

Diameter  of  pipe  in 
inches. 

Thickness  of  material 
U.  S.  standard  gauge. 

Equivalent  thickness 
in  Miches. 

'i 

t| 

II 

f 

Weight  per  lineal  foot 
in  pounds. 

1 
Price,  per  foot. 

1 

3 
4 

•  4 

18 
18 
16 

.05 

.05 
.062 

810 
607 
760 

2.25 
3.00 
3.75 

*0.205 
.35 

18 

18 
18 

12 
11 
10 

.109 
.125 
.14 

295 
337 
378 

25.25 
29.00 
32.50 

$1.90 
2.10 
2.40 

5 

18 

.05 

485 

3.75 

.30 

5 
5 

16 
14 

.062 
.078 

605 
757 

4.50 
5.75 

.45 
.50 

20 
20 

16 
14 

.062 
.078 

151 

189 

16.00 
19.75 

1.26 
154 

6 
6 
6 

18 
16 
14 

.05 
-062 
.078 

405 
505 
630 

'  4.25 
.5.25 
6.50 

.44 

.50 
.56 

20 
20 
20 

11 
10 

8 

.125 
.14 
.171 

304 
340 
415 

31.50 
35.00 
45.50 

2.25 
2.50 
3.40 

7 
7 

7 

18 
16 
14 

05 
.062 
.'078 

346 
433 
540 

4.75 
6.00 
7.50 

.50 
.56 
.63 

22 
22 
22 

16 
14 
12 

.062 
.078 
109 

"138" 
172 
240 

17.75 
22.00 
30.50 

1.40 
1.70 
2.25 

8 
8 
8 

16 
14 

12 

.062 
.078 
.109 

378 
472 
660 

7.00 
8.75 
12.00 

.65 
.75 
.94 

22 
22 
22 

11 
10 
8 

.125 
.14 
171 

276 
309 
376 

34.50 
39.00 
50.00 

2.40 
.  2.80 
3.75 

9 
9 
9 

16 
14 
12 

.062 
.078 
.109 

336 
420 

587 

7.50 
9.25 
12.75 

.69 
.88 
1.06 

24 
24 
24 

14 
12 
11 

.078 
.109 
.125 

Idtf 

220 
253 

23.75 
32.00 
37.50 

1.80 
2.35 
2.70 

10 
10 
10 

16 
14 
12 

.062 
.078 
.109 

307 
378 
530 

8.25 
10.25 
14.25 

.72 
.82 
1.00 

24 
24 
24 

10 
8 
6 

.14 
.171 
.20 

283 
346 
405 

42.00 
50.00 
59.00 

2.95 
3.50 
4.30 

10 
10 

11 
10 

.125 
.14 

607 
680 

16  25 
18.25 

1.25 
1.50 

26 
26 

14 
12 

.078 
.109 

145 
203 

25.50 
35.50 

2.00 
2.59 

11 
11 
11 
11 

16 
14 
12 
11 

.062 
.078 
109 
.125 

275 
344 
480 
553 

9.00 
1100 
15.25 
17.50 

.75 
.94 
1.25 
1.44 

26 
26 
26 
26 

11 
10 
8 
6 

.125 
.14 
.171 
.20 

233 
261 
319 
373 

39.50 
44.25 
54.00 
64.00 

2.87 
3.10 
3.85 
4.75 

11 

10 

.14 

617 

19.50 

1.62 

28 

14 

.078 

135 

27.25 

2.12 

12 
12 
12 
12 
12 

16 
14 
12 
11 
10 

.062 
.078 
.109 
.125 
.14 

252 
316 
442 
506 

567 

10.00 
12125 
17.00 
19.50 
21.75 

.82 
1.00 
1.38 
1.50 
1.69 

28 
28 
28 
28 
28 

12 
11 
10 
8 
6. 

.109 
.125 
.14 
.171 
.20 

188 
216 
242 
295 
346 

38.00 
42.25 
47.50 
58.00 
6900 

2.75 
3.00 
3.20 
4.15 
5.00. 

13 
13 
13 
13 
13 

16 
14 
12 
11 
10 

.062 
.078 
.109 
.125 
.14 

233 
291 
407 
467 
522 

10.50 
13.00 
18.00 
20.50 
23.00 

.90 
1.12 
1.50 
1.65 
1.80 

30 
30 
30 
30 
30 

12 
11 
10 
8 
6 

.109 
.125 
.14 
.171 
.20 

176 
202 
226. 
276 
323 

39.50 
45.00 
50.50 
61.75 
73.00 

2.90 
3.15 
350 
4.30" 
5.25 

14 

16 

.062 

216 

11.25 

.98 

30 

V* 

.25 

404 

9000 

6.50 

14 
14 
14 
14 

14 
12 
11 
10 

.078 
.109 
.125 
.14 

271 

878 
433 
485 

14.00 
19.50 
22.25 
25.00 

1.17 
1.57 
1.72 
1.95 

36 
36 
36 
36 

11 

10 

fe 

.125 
.14 
.187 
25 

168 
189 
252 
337 

54.00 
60.50 
81.00 
109  00 

3.80 
4.30 
5.75 
7.60 

15 
15 

16 

.062 
078 

202 
252 

11.75 
14  75 

.96 
1  28 

36 

*/:* 

.312 

420 

135.00 

9.50 

15 
15 
15 

12 
11 
10 

.109 
.125 
.14 

352 
405 
453 

20.50 
23.25 
26.00 

1.75 
1.95 
2.10 

40 
40 
40 

10' 

:«•• 

.14 
.187 
.25 

170 
226 
303 

67.50 
90.00 
12000 

4.75 
640 
8.40 

16 
16 

16 
14 

.062 
.078 

190 
237 

13.00 
16.00 

1.05 
1.20 

40 

IK 

.375 

455 

180.00 

12.00 

16 
16 
16 

12 
11 
10 

.109 
'  .125 
14 

332 
379 
425 

22.25 
24.50 
28.50 

.1.70 
1.85 
2.00 

42 
42 
42 

10 

fe 

.14 
M7 
.25 

162 
216 

289 

71.00 
94.50 
126.00 

5.05 
700 
9.50 

•is 

IS 

•16 
14 

.  .062 
.078 

168 
210 

14.75 
18.50 

1.20 
1.40 

42 
1  42 

Vie 
•/• 

.312 
.375 

360 
435 

158.00 
190.00 

12.00 
15.00 

Table  II 


APPLIED    HYDRAULICS 


61 


located  a  few  feet  below  the  forebay  for  counteracting 
water  hammer  near  the  power  house. 

The  factor  of  safety  for  nearly  all  material  used  in  pipe 
lines  under  high  heads  ranges  from  five  to  six,  and  it  is 
occasionally  eight.  (Table  II.  ) 

Auxiliaries  of  Pipe  Systems:  Fore  bays,  Sand  Boxes,  and 
"  Grizzles."  —  Forebays  have  two  functions ;  namely,  to 


Fig.  23.    Type  of  Sand  Box  used  in  Western  Practice 

allow  the  water  to  settle  before  it  is  admitted  to  the  press- 
ure pipe,  so  that  sand  and  silt  will  be  deposited,  and  to 
permit  submerging  the  intake  of  the  pressure  pipe.  Fore- 
bays  are  constructed  either  of  concrete  masonry  or  a  natural 
basin  is  sometimes  taken  advantage  of  by  constructing  an 
earthen  dam  across  a  canyon  or  ravine,  the  bottom  of 
which  is  sometimes  paved  with  cement. 


62     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Sand  boxes  are  placed  at  the  ends  of  water-conducting 
systems  to  prevent  sand  from  entering  the  nozzles  and 
buckets  of  water  wheels.  They  usually  consist  of  chambers, 
or  box-like  compartments,  having  a  considerable  slope  from 
the  point  where  the  water  enters. 

Each  of  the  dividing  walls  of  the  chambers  except  the 
middle  one  is  designed  to  be  several  feet  below  the  surface 
of  the  water.  The  middle  wall  is  slightly  higher  than  the 
water  surface,  and  thus  allows  the  water  to  pass  through  a 
gate  into  the  connecting  pipe  line.  Fig.  23  shows  a  sand 
box  of  this  construction.  At  the  lower  end  of  the  com- 
partments is  a  plug  valve  provided  with  a  stem  that  runs 
up  through  the  water  to  a  board  walk  above.  The  valve 
is  lifted  by  a  block  and  tackle,  which  opens  the  orifice 
in  the  bottom  of  a  compartment,  and  by  turning  water 
into  each  compartment  the  box  can  be  quickly  cleared  of 
sand. 

Sand  boxes  are  sometimes  made  of  two  parallel  hoppers 
with  sluice  gates  in  the  bottom  through  which  accumulated 
sand  and  silt  can  be  expelled.  Water  is  passed  through 
one  hopper  while  the  other  is  being  emptied. 

"  Grizzles  "  are  devices  for  removing  leaves,  debris,  etc., 
from  water-conducting  systems. 

Conduits  and  Canals.  —  The  term  "  conduit "  as  generally 
applied  in  hydraulics  means  a  channel  of  any  shape,  open 
or  closed,  and  lined  with  masonry,  concrete,  or  timber. 
The  word  is  also  applicable  to  large  pipes  made  of  metal  or 
wood. 

The  term  "canal"  is  applied  to  a  conduit  excavated  in 
the  earth  and  without  masonry  or  other  artificial  lining. 
A  common  name  for  a  supply  canal  is  " head-race" 

Conduits  and  canals  are    more  generally  employed  for 


APPLIED    HYDRAULICS  63 

conveying  water  to  hydraulic  plants  than  any  other  form 
of  conducting  medium.  Their  usual  shape  is  rectangular, 
but  they  may  be  of  either  trapezoidal  or  triangular  cross- 
section. 

In  regions  where  the  geological  formation  or  character 
of  the  soil  would  occasion  considerable  loss  of  water 
through  seepage  into  the  soil,  it  is  considered  more  advan- 
tageous, especially  if  the  conducting  channel  is  long,  to 
line  it  with  concrete  or  timber. 

When  a  canal  pure  and  simple  is  used  to  convey  water, 
the  sides  and  bottom  are  generally  puddled  with  clay  to 
prevent  percolation  of  the  water  through  the  soil.  In  some 
cases  this  is  accomplished  by  sending  through  a  sediment  of 
clay  with  the  water.  This  is  continued  until  the  walls  and 
bottom  of  the  canal  are  well  plastered  with  the  clay. 

Concrete  pipe  or  conduit  is  usually  constructed  of  Port- 
land cement  in  sections  two  or  three  feet  long  and  from 
one  and  a  half  to  two  and  a  half  inches  thick.  In  the  con- 
ducting systems  of  some  Pacific  coast  hydro-electric  plants, 
the  material  used  in  the  construction  of  concrete  conduits 
is  the  natural  gravel  and  sand  taken  from  the  wash  of  the 
stream,  with  Portland  cement  as  the  binding  material. 

When  the  sections  of  pipe  are  completed  they  are  cured 
for  a  season  on  the  spot.  And  when  the  pipe  is  made  in 
ravines  or  canyons,  as  is  frequently  the  case,  the  sectio'ns 
are  hoisted  by  means  of  a  steel  cable  to  the  trench  grade 
on  the  mountain  side  above. 

Conduits  and  canals  should  receive  the  water  from  the 
reservoir  in  a  way  that  will  occasion  no  loss  by  leakage, 
and  so  that  the  mouth  of  the  channel  can  be  tightly  closed 
if  desired.  Means  must  also  be  adopted  to  prevent  leaves, 
trash,  gravel,  or  sand  from  entering  the  channel. 


64     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


BIBLIOGRAPHY 

Water  Power.  Frizell.  Third  Edition.  Wiley  &  Sons.  New  York. 
1903. 

Design  and  Construction  of  Dams.  Wegmann.  Fourth  Edition. 
Wiley  &  Sons.  1899. 

Reservoirs  for  Irrigation,  Water  Power,  etc.  Schuyjer.  Wiley  & 
Sons.  New  York.  1901. 

A  Treatise  on  Masonry  Construction.  Baker.  Ninth  Edition. 
Wiley  &  Sons.  New  York.  1899. 

A  Method  for  Determining  the  Supply  from  a  Given  Watershed. 
Greenleaf.  Engineering  News.  Volume  33.  Page  238. 

A  Form  of  Mass  Diagram  for  Studying  the  Yield  of  Watersheds. 
Horton.  Engineering  Record.  1897.  Volume  36.  Page  285. 

Instructions  for  Installing  Weirs,  Measuring  Flumes  and  Water 
Registers.  Johnson.  Engineering  News.  August  29,  1901.  Page  131. 

Commercial  Value  of  Water  Power  per  Horse  Power  per  Annum. 
Transactions  American  Society  Mechanical  Engineers.  .  Abstracted  in  En- 
gineering News.  January  22,  1903. 

Stave-Pipe.  A.  L.  Adams.  .  Transactions  American  Society  Civil 
Engineers.  18.98.  Page  676. 

Diagram  Giving  Discharge  of  Pipes  by  Kutter's  Formula.  Greg- 
ory. Engineering'  Record.  Volume  42. 

Manufacture  and  Inspection  of  Cast-iron  Pipe.  Wiggen.  Journal 
Association  of  Engineering  Societies.  May,  1899.  Page  209. 

Design  of  American  Dams.     Engineering  Record.     February  20,  1902. 

Wooden  Stave  vs.  Riveted  Pipe.  Journal  Association  of  Engineering 
Societies.  Pages  239-262.  Philadelphia.  1898. 


CHAPTER  III 

HYDRAULIC   MACHINES  AND   ACCESSORY 
APPARATUS 

Hydraulic  Machines.  Distinction  between  a  Turbine 
and  a  Water  Wheel.  —  When  water  is  admitted  to  only 
one  part  of  the  circumference  of  a  hydraulic  motor  the 
machine  is  termed  a  water  wheel.  When  water  is  admitted 
around  the  entire  periphery  of  a  hydraulic  motor  the  ma- 
chine is  termed  a  turbine. 

In  either  case  the  rotation  of  the  wheel  is  produced  by 
the  weight  of  water  falling  from  a  higher  to  a  lower  level, 
or  by  dynamic  reaction  due  to  a  change  in  velocity  and 
direction  -of  a  stream. 

According  to  the  manner  in  which  they  operate,  turbines 
are  divided  into  two  general  classes,  namely,  "impulse" 
and  "reaction  "  turbines.  The  essential  difference  between 
the  two  is  that  in  an  impulse  turbine  water  enters  the 
machine  with  a  velocity  due  to  the  head  at  the  point  of 
entrance  in  the  same  manner  that  it  does  from  the  nozzle 
which  actuates  the  impulse  wheel,  whereas  in  a  reaction 
turbine  the  velocity  of  the  entering  water  may  be  greater 
or  less  than  that  due  to  the  head  on  the  entrance  orifices  ; 
like  the  reaction  wheel  it  is  influenced  by  the  speed  of  the 
water.  The  reason  for  this  is  that  the  hydrostatic  pressure 
of  the  water  is  largely  transmitted  to  the  rotating  wheel  — 
that  is,  if  the  spaces  between  the  vanes  or  buckets  are 
entirely  filled. 

It  is  feasible  to  make  any  turbine  work  either  as  a  reaction 
or  as  an  impulse  machine.  By  actuating  it  so  that  the 

6s 


66     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


water  passes  through  the  vanes  without  entirely  filling 
them,  the  turbine  becomes  an  impulse  machine.  If,  on  the 
other  hand,  the  entering  water  is  obliged  to  fill  all  the 
buckets,  the  turbine  becomes  a  reaction  machine. 

It  is  manifest  from  the  foregoing  definitions  that  the 
buckets  of  an  impulse  turbine  are  considerably  smaller 
than  those  of  the  reaction  type. 

In  order  that  the  entire  energy  of  the  water  be  utilized, 


MOVING  WHEEL 

Fig.  24.    Outward-Flow  Turbine 


F1XK)  Gl/JPE  PASSAGES 

Fig.  25.    Inward-Flow  Turbine 


the  vanes  or  buckets  of  turbines  are  curved  tangentially, 
so  that  the  water  may  react  upon  the  surfaces  and  deliver 
as  much  energy  as  possible. 

Kinds  of  Turbines. —  Turbines  are  classified  according 
to  the  way  in  which  water  is  passed  through  them  into 
"  outward-flow,"  "  inward-flow,"  and  "  downward-flow  "  tur- 
bines. 

In  an  outward-flow  turbine  water  enters  around  the 
complete  inner  periphery  of  the  runner  and  is  discharged 
around  the  entire  outer  periphery.  In  an  inward-flow  tur- 
bine the  motion  of  the  water  is  exactly  opposite. 

In  the  downward-flow  turbine  water  is  admitted  around 


HYDRAULIC    MACHINES  67 

all  the  upper  annular  openings,  and  is  shot  downward 
between  the  rotating  vanes,  passing  out  through  the  lower 
annulus. 

The  normal  speed  of  an  impulse  turbine  is  somewhat 
lower  than  that  of  a  corresponding  reaction  turbine  oper- 
ating under  the  same  head,  but  the  entrance  velocity  of 
the  water  is  considerably  greater  in  the  impulse  type, 
which  means  that  consider- 

,    ,  ,  .     ,    ,  FIXED  GUIDE  PASSAGES 

ably    more    energy    is    liable       ~T j T — h T T T- 

to  be  wasted  by   shock    and       \      \      \      \      \       \      \ 
foam.  \\\V\     \    \ 


MOVING  WHEEL 


Fig.     24     shows    an     out-      Fie  ^  Downward.Flow 
ward-flow    turbine,    Fig.     25 

an    inward-flow    turbine,    and    Fig.    26    a   downward-flow 
turbine. 

Conditions  to  which  Impulse  and  Reaction  Turbines 
are  Adapted. —  The  type  of  hydraulic  machine  which 
should  be  adopted  in  any  particular  case  depends  upon  the 
height  of  head  which  is  to  be  utilized.  In  general,  for  low 
heads,  —  i.e.,  up  to  45  feet,  — the  impulse  or  "  American  " 
type  of  turbine,  mounted  on  a  horizontal  or  vertical  shaft, 
with  open  flume  (and  usually  with  draft  tube),  should  be 
employed. 

For  moderate  heads,  ranging  from  45  to  400  feet,  the 
reaction  turbine  (with  radial  inward  flow),  mounted  on  a 
horizontal  shaft  and  fitted  with  a  cast-iron  case  and  draft 
tube,  should  be  employed. 

For  high  heads,  i.e.,  those  ranging  from  400  to  2,000 
feet  or  over,  the  Pelton  type  of  wheel  or  the  radial  out- 
ward-flow machine,  mounted  on  a  vertical  shaft  and  con- 
tained in  a  cast  or  wrought  iron  case,  with  draft  tube, 
should  be  used 


68     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

A  reaction  turbine,  as  stated  previously,  is  rotated  by  the 
dynamic  pressure  of  moving  water,  which  may  also  be 
more  or  less  under  static  pressure.  Hence,  the  particular 
sphere  of  work  to  which  the  reaction  machine  is  suited  is 
under  conditions  where  a  large  quantity  of  water  under  a 
moderate  head  must  be  handled. 

As  regards  the  conditions  for  which  the  impulse  wheel 
is  well  adapted,  it  may  be  said  in  general  that  for  heads 
ranging  from  100  feet  upwards  this  type  of  wheel  is  the 
only  practical  form,  capacity  and  size  being  equal. 

When  a  hydraulic  machine  is  driving  an  electric  gene- 
rator it  becomes  imperative  to  maintain  a  practically  con- 
stant speed  irrespective  of  changes  in  the  load.  In  this 
respect  a  reaction  turbine  cannot  compare  with  an  impulse 
water  wheel,  since  a  change  in  its  speed  involves  a  consid- 
erable loss  in  efficiency.  In  an  impulse  wheel  water  can 
be  admitted  through  a  part  of  the  guides,  which  with  a 
reaction  turbine  is  manifestly  infeasible. 

The  efficiency  of  an  impulse  wheel  is  not  appreciably 
diminished  by  a  partial  closing  of  the  admission  gates,  but 
with  a  reaction  turbine  the  abrupt  increase  of  cross-section 
beyond  the  partly  closed  gates  causes  a  considerable  diminu- 
tion of  efficiency.  The  normal  speed  of  an  impulse  wheel 
is  constant  for  all  positions  of  the  gate.  With  a  reaction 
turbine  the  speed  is  considerably  less  at  partial  than  at 
maximum  gate. 

Efficiencies  of  Hydraulic  Machines. — The  efficiency  of 
hydraulic  motors  depends  upon  the  following  conditions  : 
(i)  The  water  should  enter  the  machine  without  producing 
appreciable  shock.  (2)  It  should  be  discharged  from  the 
machine  at  a  low  velocity.  (In  general  the  lower  the 
velocity  in  the  tail  race,  the  greater  the  amount  of  useful 


HYDRAULIC    MACHINES 


69 


work  which  the  motor  has  abstracted  from  it.)  Or  the 
water  should  enter  the  buckets  without  shock  and  leave 
without  velocity.  (3)  The  buckets  or  vanes  of  the  turbine 
should  be  so  curved  as  to  receive  the  full  impact  of  the 
nozzle  jet.  (4)  The  water  supply  should  be  free  from 
sediment,  sand,  leaves,  or  other  organic  matter.  (5)  The 
rotating  member  of  the  turbine  should  revolve  in  its  bear- 
ings with  the  minimum  of  friction. 

The  efficiencies  of    American-made  hydraulic  machines 
range  from  65  to  85  per  cent,  depending  upon  the  design, 


EFFICIENCY  TEST  OF  RISDON  WATER  WHEEL 
AT  COLGATE  STATION 


Tl         C 

>     c 

>     c 

c 

'     c 

5    d 

1 

I  1 

^ 

>         tf 

H            ^ 

1                   L 

§         t 

?    s 

;  t 

i  < 

i  ? 

i  ? 

s     S 

\     \ 

J     I 

S      S 

?  1 

a  s 

3     1 

S     9 

< 

l£ 

1     8 

Ho 

N 

SO 

,.  •— 

.  —  - 

,  —  — 

__—  -* 

.^n  •*• 

—.     •*• 

^   -* 

—     — 

>—  — 

__      — 

Id 

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fA 

Fig.  27 

output,  and  conditions  of  operation.  The  majority  of 
machines  of  moderate  output  will  not  exceed  70  per  cent 
in  efficiency.  Fig.  27  shows  the  efficiency  curve  of  a 
3,000  horse-power  Risdon  impact  wheel. 

The  importance  and  desirability  of  employing  the  most 
efficient  turbine  commensurate  with  the  permissible  outlay 
cannot  be  over-estimated.  In  cases  where  the  water  supply 
is  uncertain  or  limited  it  becomes  almost  imperative  to 


70     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

adopt  a  machine  which  will  transform  the  kinetic  energy 
of  the  water  into  the  maximum  mechanical  power.  Es- 
pecially is  this  true  in  cases  where  the  water  is  bought  or 
power  sold. 

In  the  Engineering  News  of    December    4,    1902,   Mr. 
John    W.    Thurso  admirably  shows  the  great  importance 


Fig.  28.      Samson  Niagara  Type  Turbine 

of  using  an  efficient  turbine.  He  says,  "  Supposing  that 
power  is  sold  at  $15  per  year  for  an  effective  mechani- 
cal horse-power  at  the  turbine  shaft,  and  that  the  water 
supply  is  limited.  The  amount  of  water  required  to  de- 
velop one  effective  horse-power  with  70  per  cent  efficiency 
will  give  1.143  horse-power,  worth  $17. 14  per  year,  with 
80  per  cent  efficiency. 

"  The  difference  of  $2.14   in  favor  of  the  turbine  with 
higher  efficiency  is  equal  to  an  interest  of   1 5  per  cent  as 


HYDRAULIC    MACHINES  7 1 

above  on  $14.27  ;  or  a  1,000  horse-power  turbine  giving  80 
per  cent  efficiency  could  cost  $14,267  more  than  a  tur- 
bine giving  70  per  cent  efficiency  witliout  being  more  ex- 
pensive." 

Types  of  American  Turbines.  —  Fig.  28  shows  one  form 
of  the  Samson  turbine  made  by  the  James  Leffel  Com- 
pany. It  is  of  the  double-discharge  horizontal  form,  and  is 


•BB^*1 , .      i 

Fig.  29.     High-Head  Heavy  Duty  Turbine 

called  the  Niagara  design.  This  type  is  usually  fitted  with 
one  runner  and  two  similar  sets  of  buckets.  The  entering 
water  is  equally  divided  between  the  two  sets  of  guides 
and  is  discharged  in  opposite  horizontal  directions.  This 
form  of  turbine  is  fitted  with  an  outer  casing,  thus  afford- 
ing an  easy  circulation  of  water  around  the  guides  on  the 
runner.  Water  is  admitted  to  the  casing  either  from  below 
or  at  any  desired  angle  from  a  horizontal  or  vertical  line 
on  top. 

The  shafts  revolve  in  ring-oiled  bearings  supported  by 


72     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


heavy  iron  -bridge-trees.     The  illustration  shows  a  2,400 
horse-power  machine  for  direct  connection. 

Fig.  29  shows  a  high  head,  heavy  duty,  center  dis- 
charge, horizontal  shaft  Samson  turbine.  It  consists  of 
two  56-inch  turbines  mounted  on  a  bronze  shaft  and  fitted 
with  bronze  runners  and  balanced  steel  gates. 

The  type  of  runner  used  on  Samson  turbines  is  shown 
in  Fig.  30,  which  is  an  illustration  of  the  vertical  shaft 

type.  The  runner  is  made  up 
of  two  distinct  forms  of  wheels 
which  have  different  diameters. 
Each  set  of  buckets  comprising 
a  wheel  receives  its  separate 
quantity  of  water  from  the  same 
set  of  guides,  and  discharges  to 
the  outlet ;  the  water  does  not 
act  twice  upon  the  combined 
wheel. 

.  Fig.  $ia  shows  a  5  5 -inch  Vic- 
tor high  pressure  turbine  made 
by  the  Platt  Iron  Works.  This 
turbine  develops  8,000  horse- 
power under  a  63O-foot  head  and 
is  controlled  by  a  Lombard  gov- 
ernor. The  illustration  shows  the 
water  supply  connection  below  the  floor  level,  also  the 
by-pass  valve. 

Fig.  31^  shows  this  type  of  turbine  coupled  to  an 
alternator. 

The  Victor  machine  is  a  mixed-flow  type,  water  entering 
radially  inward  at  the  circumference  and  discharging 
downwards  and  outwards.  The  whole  depth  of  the  wheel 


Fig.  30.     Runner  of  Samson 
Turbine 


HYDRAULIC    MACHINES  73 

proper  is  occupied  by  the  buckets,  which  are  deep  axially, 
thus  giving  large  capacity  for  its  size. 

Water  supply  to  turbines  is  regulated  by  two  types  of 
gate,  one  of  which  is  termed  the  register  gate  and  the 
other  the  cylinder  gate.  The  former  admits  water  to 
the  turbine  by  turning  about  the  axis  of  the  wheel,  thus 


Fig.  sia.     Victor  High-Pressure  Turb-'ne 

opening  the  passage  wider  and  wider  as  it  is  turned  more 
and  more,  and  at  the  same  time  giving  direction  to  the 
water.  The  cylinder  gate  is  the  preferable  form  when 
the  water  supply  is  variable  or  when  the  work  is  variable  : 
the  cylinder  gate  is  also  better  adapted  to  low  and  medium 
heads. 

Fig.  32  shows  a  pair  of  42-inch  McCormick  turbines  made 
by  the   S.  Morgan  Smith  Company.     The    machines  are 


74     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

designed  for  direct  connection  to  an  electric  generator,  and 
develop  4,000  horse-power  at  300  revolutions  per  minute 
under  a  72-foot  head.  The  illustration  also  shows  a  single 
400  horse-power  turbine  for  driving  the  generator  exciter. 
Water  Wheels  —  Principles  of  Operation :  Features  upon 
which  Speed  and  Power  Depend.  —  A  hydraulic  machine, 
as  has  been  already  stated,  is  known  as  a  " water  wheel" 


Fig.  3ib.     A  1,000  Horse-Power  Turbine  Coupled  to  Alternator 

when  water  is  admitted  to  one  part  of  its  circumference. 
Since  this  type  is  driven  by  the  impact  of  a  jet  or  jets  of 
water  against  buckets  mounted  on  the  periphery  of  a  wheel 
it  is  termed  an  "  impulse  wheel." 

In  general  the  impulse  wheel  is  the  most  practical  form 
of  machine  that  can  be  employed  when  the  head  is  above 
100  feet,  and  for  very  high  heads  it  is  the  only  type  of 
machine  that  can  be  employed.  The  buckets  of  water 


HYDRAULIC    MACHINES  75 

wheels  are  curved  tangentially  or  ellipsoidally,  the  object 
in  either  case  being  to  oblige  the  water  to  react  upon  the 
bucket  surfaces  so  as  to  give  up  the  maximum  amount  of 
its  energy. 

Water  is  conducted  to  an  impulse  wheel  through  the 
various  types  of  artificial  channels  described  in  the  preceding 
chapter,  and  is  delivered  to  the  buckets  through  a  nozzle, 
the  end  of  which  is  fitted  with  a  cylindrical  tip,  the  diameter 


jj 

L 


Fig.  32.    A  Pair  of  4,000  Horse-Power  McCormick  Turbines 

of  which  is  proportional  to  the  head  of  water  and  the  amount 
of  power  to  be  developed.  Since  tips  of  different  diameters 
can  be  screwed  into  the  nozzle  it  is  thus  possible  to  vary 
the  power  of  the  wheel  from  the  maximum  (limited  by  the 
size  of  the  buckets)  down  to  a  small  percentage  of  the 
rated  capacity.  The  use  of  varying  sizes  of  nozzles  thus 
permits  of  maintaining  a  nearly  uniform  efficiency  at  all 
stages  of  load. 

When  it  is  desired  to  double  or  treble  the  output  of  a 
water  wheel  without  increasing  its  diameter,  two  or  three 
nozzles  are  employed,  the  consumption  of  water  being 
correspondingly  increased,  of  course. 


76     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  power  of  a  water  wheel,  strictly  speaking,  does  not 
depend  upon  its  dimensions,  but  upon  the  head  and  quantity 
of  water  supplied  to  it. 

The  speed  of  a  water  wheel  depends  upon  its  diameter, 
and  when  operating  under  a  given  head  the  number  of 
revolutions  which  it  maintains  should  be  constant,  regardless 
of  the  amount  of  power  it  is  developing. 

Water  wheels  are  constructed  to  operate  in  either  a 
vertical  or  horizontal  plane,  the  horizontal  type,  however, 
being  more  commonly  employed.  In  the  horizontal  type 
the  wheel  is  supported  on  a  shaft  running  in  journal  boxes, 
the  entire  running  mechanism  being  inclosed  in  an  iron 
casing  divided  in  a  horizontal  plane.  When  the  wheel  is 
mounted  in  a  vertical  plane  the  shaft  is  provided  with  a 
step  and  thrust  bearing. 

The  buckets  of  water  wheels  are  constructed  of  phosphor 
bronze,  cast  steel,  or  cast  iron,  depending  upon  the  conditions 
under  which  the  wheel  must  operate,  —  i.e.,  the  head  of  water 
and  the  character  of  the  water  supply,  its  freedom  or  non- 
freedom  from  abrasive  material  in  suspension. 

Power  of  a  Water-  Fall  Utilized  by  a  Hydraulic  Machine. 
—  Representing  the  pounds  of  water  delivered  per  second 
to  a  hydraulic  machine  by  W,  and  considering  //  as  its 
effective  head  in  feet  as  it  enters  the  machine  (the  head  // 
may  be  due  to  either  pressure  or  velocity  or  to  pressure  and 
velocity  combined),  then  the  theoretical  power  in  foot-pounds 
per  second  of  the  water  is 

K=Wh, 

and  the  theoretical  horse-power  of  the  water  as  it  enters  the 
machine  is 


55 


HYDRAULIC    MACHINES  77 

On  account  of  losses  in  impact,  friction,  etc.,  the  actual 
horse-power  of  a  hydraulic  machine  is  considerably  less 
than  the  theoretical  horse-power  of  the  water. 

Using  k  to  indicate  the  work  delivered  by  a  hydraulic 
machine,  and  e  its  efficiency,  then, 

k         k  h.p. 

e  =—  =-TTTT,     and     e  = 


K  ~  Wti  H.P? 

a  fair  average  for  wheels  of  moderate  output  being  75  per 
cent.  The  average  efficiency  of  wheels  of  even  compara- 
tively large  output  is  rarely  over  78  per  cent,  and  their  all- 
day  efficiency  will  barely  exceed  60  per  cent. 

Effective  Head  on  an  Impulse  Wheel.  —  When  water  is 
conducted  through  a  nozzle  or  a  pipe  line  to  a  water 
wheel,  the  head  h  is  not  the  maximum  head,  since  a  con- 
siderable portion  of  this  latter  head  is  lost  in  friction  in  the 
pipe  system.  Hence  the  head  on  the  turbine  or  water 

F2 
wheel  is  really  the  velocity  head,  • — ,  of  the  jet. 

Having  determined  the  value  of  V  from  the  discharge  q, 
and  the  area  of  the  cross-section  of  the  stream,  the  effec- 
tive .head  on  an  impulse  wheel  is 


2g         2gav 

in  which  q  is  the  discharge,  and  a  the  area  of  its  cross- 
section. 

Speed  Regulation  of  Water  Wheels  and  Turbines.  —  The 
three  general  methods  for  regulating  the  speed  of  water 
wheels  are : 

(i)  By  means  of  a  deflecting  nozzle;  (2)  by  a  plug 
nozzle;  and  (3)  by  the  use  of  a  cut-off  hood.  In  each 


78     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

method  the  controlling  device  is  always  actuated  by  some 
form  of  automatic  governor,  the  function  of  which  is  to 
adjust  the  position  of  the  device  to  suit  the  demands  of  the 
load. 

The  deflecting  nozzle  is  usually  of  cast  iron  and  fitted 
with  a  ball  and  socket  joint,  which  permits  of  its  being 
raised  or  lowered,  thereby  throwing  the  nozzle  on  or  off 
the  buckets.  Thus  the  power  output  of  the  wheel  is  in- 
creased or  decreased  to  meet  a  change  of  load,  and  the 


Fig.  33.     Deflecting  Nozzle 

speed  is  kept  uniform.  A  modification  of  this  speed-regu- 
lating device  consists  of  a  plate  which  deflects  the  stream, 
the  nozzle  being  kept  stationary.  Fig.  33  shows  a  deflect- 
ing nozzle. 

A  plug  nozzle  is  a  nozzle  body  fitted  with  a  concentric 
tapered  plug.  By  changing  the  position  of  this  plug  a 
change  is  produced  in  the  discharge  area  of  the  nozzle, 
thereby  varying  the  amount  of  water  consumed  by  the 
wheel,  the  power  output  being  governed  accordingly. 

A  cut-off  hood  consists  of  a  spherical  plate  fitted  tightly 
over  the  end  of  the  nozzle.  Variation  in  the  position  of  the 


HYDRAULIC    MACHINES  79 

hood  produces  a  change  in  the  discharge  area  of  the  nozzle, 
thus  varying  the  power  of  the  wheel. 

The  speed  regulation  of  turbines  is  accomplished  almost 
universally  by  means  of  gate  valves  controlled  by  some  form 
of  governor,  the  function  of  the  governor  being  to  open  or 
close  the  water  supply  orifice  to  an  extent  corresponding 
to  the  increased  or  decreased  demand  for  power. 

Perfect  speed  regulation  of  hydraulic  machines  is  im- 
possible, owing  to  two  limitations  :  (i)  Such  limitations  as 
are  imposed  by  the  governor  itself,  and  (2)  those  imposed 
by  the  inertia  of  the  masses  upon  which  the  governor  acts 
to  control  the  speed. 

Governors  —  Requisites  of  a  Good  Governor.  —  The 
most  important  desiderata  which  a  good  governor  should 
possess  are  simplicity,  ability  to  regulate  closely  the  speed 
of  the  hydraulic  machine,  freedom  from  racing  and  hence 
avoidance  of  unnecessary  movements  of  the  gate,  freedom 
from  all  shocks  and  jerky  movements,  adaptability  to  all 
kinds  of  plants,  reliability  of  operation,  and  low  cost  of 
maintenance. 

The  chief  limitations  possessed  by  all  forms  of  governors 
are  due  to  the  fact  that  there  must  be  a  speed  variation  to 
some  degree  before  the  governor  can  begin  to  operate,  and 
a  definite  time  is  required  to  adjust  the  gate  to  its  new 
position.  Moreover,  the  initial  change  must  become  ap- 
preciable before  the  governor  operates  the  gate  at  its 
maximum  speed,  but  the  appliances  used  to  prevent  the 
overspeeding  of  the  gate  invariably  exercise  a  dampening 
effect  upon  the  speed  of  the  gate  movement  while  it  is 
motive. 

The  secondary  limitations,  or  those  due  to  the  inertia  of 
the  masses  to  be  moved,  are  far  more  complex.  These  are 


80     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

due  to  the  sluggishness  of  movements  of  the  various  com- 
ponents of  the  gate,  such  as  the  shafts  and  the  rigging, 
and  to  the  inertia  of  the  water  to  be  controlled. 

Kinds  of  Governors  —  Principles  of  Operation.  — Gover- 
nors for  regulating  hydraulic  machines  are,  (i)»  those  oper- 
ated by  the  pressure  of  a  fluid,  which  may  be  oil  or  water  ; 
(2)  mechanically  operated  ;   (3)  electro-mechanical,  or  (4 
induction  motor  governors. 

Governors  of  the  first  kind  are  generally  termed  "hy- 
draulic "  governors.  The  fluid  used  for  operation  depends 
on  the  conditions  which  must  be  met,  as  well  as  considera- 
tions of  cost  and  maintenance.  In  general  oil-pressure 
governors  are  used  for  low  heads,  while  the  water-pressure 
form  is  employed  for  heads  above  100  feet.  The  essential 
elements  of  a  hydraulic  governor  are,  a  cylinder  fitted 
with  a  shaft  or  piston  which  actuates  the  water  gate ;  a 
hydraulic  valve  or  valves  working  in  a  chamber,  and  con- 
trolling the  pressure  applied  to  the  hydraulic  cylinder  ;  a 
centrifugal  governor  for  controlling  the  movements  of  the 
main  valve ;  an  auxiliary  controlling  device  which  deter- 
mines the  amount  of  the  gate  opening  for  any  definite 
variation  of  load ;  some  form  of  anti-racing  mechanism  ; 
some  form  of  controller  for  determining  the  rate  of  speed 
at  which  the  governor  shall  operate,  and  a  power  pump 
(if  the  governor  is  of  the  oil-pressure  form). 

Mechanically  operated  governors  usually  consist  of  a 
train  of  gear  wheels,  driven  by  the  governed  unit  and  fitted 
with  a  centrifugal  speed-regulating  device  which  permits 
the  governor  to  trip  some  mechanical  device  for  moving  the 
water  gates. 

Electro-mechanical  governors  operate  by  means  of 
electro-magnets  which  throw  reciprocating  pawls  into  oper- 


HYDRAULIC    MACHINES  8l 

ation,  these  pawls  being  so  arranged  that  they  actuate  the 
regulating  mechanism  of  the  wheel. 

Governing  by  electric  (induction)  motors  has  been  suc- 
cessfully applied  in  one  or  two  Western  hydro-electric 
plants  to  small  impulse  wheels  driving  exciter  dynamos. 
The  speed  regulation  of  the  turbo-generator  unit  in  this 
case  depends  upon  the  principle  of  the  induction  motor  in 
running  below  synchronism  normally,  and  of  giving  no 
mechanical  output  of  power  when  driven  at  synchronous 
speed.  When  driven  above  synchronous  speed  by  extra- 
neous means  current  is  delivered  instead  of  consumed.  In 
the  case  under  discussion  the  motor  is  run  above  syn- 
chronism, and  thus  absorbs  the  surplus  energy  of  the  water 
wheel  over  that  demanded  by  the  exciter  dynamo.  But 
when  the  load  on  the  exciter  becomes  of  such  a  value  that 
the  water  wheel  is  unable  to  take  care  of  it,  the  motor 
ceases  to  generate  current  and  performs  its  function  of 
motor,  thus  helping  the  water  wheel.  When  the  water 
supply  of  the  wheel  is  accidentally  or  purposely  cut  off,  the 
motor  can  be  used  to  drive  the  exciter  dynamo.  Thus  it 
can  be  made  to  perform  the  function  both  of  a  water  wheel 
governor  and  a  prime  mover.  In  the  cases  where  the 
electric  motor  has  been  employed  as  a  governor  it  is 
mounted  on  the  same  shaft  with  the  water  wheel. 

Switchboard  Control  of  Governors.  —  The  control  of 
governors  from  the  switchboard  greatly  reduces  the  time 
and  labor  necessary  to  effect  a  variation  in  the  speed  of  a 
hydraulic  machine,  and  also  simplifies  the  method  of  speed 
regulation  considerably.  This  plan  of  governor  operation 
readily  enables  the  switchboard  attendant  to  start,  .stop,  or 
alter  the  speed  of  a  single  machine  or  of  all  the  machines 
under  his  care,  from  one  central  point. 


82     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


In  this  method  of  operation  a  small  alternating  current 
motor  performs  the  work  of  shortening  or  lengthening  the 
valve  stem,  instead  of  the  attendant's  fingers.  Hence  this 

dispenses  with 
the  practice  of 
having  one  man 
to  watch  the 
synchronizing 
lamps  and  an- 
other to  attend 
the  governor  and 
vary  its  speed  in 
accordance  with 
the  signals  given 
from  the  switch- 
board, so  that  the 
switchboard  at- 
tendant can  per- 
form any  or  all 
of  the  operations 
of  starting  or  stop- 
ping or  synchro- 
nizing machines 
thrown  in  paral- 

Fig.  34.     Electric  Speed  Controller  for  Governors         lei,     without     Ollt- 

side  assistance. 

Fig.  34  shows  the  electric  speed  controller  of  the  Lom- 
bard Governor  Company.  In  this  type  of  controller  a  small 
fan  motor  of  about  one  sixteenth  horse-power  is  attached 
to  a  bracket,  which  is  clamped  to  the  governor  regulating 
valve.  The  armature  shaft  of  the  motor  carries  a  small 
worm,  which  drives  a  worm  gear  on  a  vertical  pinion  shaft. 


HYDRAULIC    MACHINES  83 

The  pinion  imparts  a  rotary  motion  to  another  gear  which 
is  threaded  through  its  hub,  and  so  acts  as  a  right  and  left 
coupling  to  force  together  or  push  apart  the  two  portions 
of  a  valve  stem  upon  which  it  rotates.  The  pinion  is  made 
of  sufficient  length  so  as  not  to  interfere  with  the  up  and 
down  travel  of  the  gear.  Current  for  operation  is  obtained 
either  from  the  exciter  circuit  or  from  batteries. 

The  controlling  apparatus  consists  of  a  small  reversible 
motor  connected  by  double  reduction  worm  gearing  to  the 
bracket  supporting  the  controlling  lever  of  the  governor. 
The  motor  imparts  an  endwise  thrust  to  this  bracket,  which 
in  turn  shifts  the  position  of  the  controlling  lever,  and  thus 
causes  a  variation  of  the  speed  at  which  the  governor  has 
been  maintaining  the  turbine. 

The  switch  which  controls  the  motor,  and  which  may  be 
located  at  any  point  desired,  such  as  a  switchboard,  has  two 
buttons  for  raising  and  lowering  the  speed,  and  a  small 
thumb  switch  for  entirely  cutting  out  the  apparatus  when 
it  is  not  in  use.  The  thumb  switch  is  fitted  with  three 
contacts,  one  of  which  is  employed  for  quickly  stopping  the 
unit  without  requiring  the  attendant  to  depress  the  push 
button  while  this  is  being  done.  Automatic  cut-outs  are 
used  on  the  motor  to  prevent  its  overrunning  when  the 
lever  has  reached  its  limit  of  movement. 

Types  of  American  Governors. —  A  type  of  fluid  pressure 
governor  quite  extensively  used  in  hydro-electric  plants  is 
the  Lombard,  made  by  the  Lombard  Governor  Company,  of 
Boston.  Fig.  35  shows  the  type  "  D  "  Lombard  oil  pressure 
governor.  The  cylindrical  tank  which  is  contained  under 
the  bed  of  the  governor  is  divided  into  two  compartments, 
the  dividing  partition  being  located  at  the  point  indicated 
by  the  row  of  rivets. 


84     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  larger  part  of  the  cylinder  (to  the  left)  is  filled  about 
half  full  of  oil,  while  the  upper  part  of  the  larger  compart- 
ment of  the  pressure  tank  is  filled  with  air  under  a  pressure 
of  approximately  200  pounds  per  square  inch. 

The  smaller   compartment  of   the    cylinder   contains  a 


Fig-  35-     Oil  Pressure  Governor  for  Moderate  Sized  Turbines 

vacuum.  Both  pressure  and  vacuum  are  constantly  main- 
tained by  means  of  a  pump  placed  on  the  farther  side  of 
the  governor  bed  and  driven  by  the  larger  pulley,  this  being 
belted  so  as  to  revolve  continuously  when  the  governor  is 
in  operation. 

The   movement    of   the  water  wheel  gates  takes  place 


HYDRAULIC    MACHINES 


when  oil  from  the  pressure  tank  is  let  in  on  one  side  of  the 
piston.  Immediately  this  occurs,  oil  on  the  other  side  of 
the  piston  is  discharged  into  the  vacuum  tank,  from  whence 


Fig.  36.    Governor  for  Impulse  Water  Wheels 

it  is  at  once  pumped  into  the  pressure  tank.  The  piston 
rod  is  terminated  in  a  rack  which  is  geared  positively  to  the 
gate  shaft.  A  full  stroke  of  the  piston  rod  completely 
opens  or  closes  the  water  wheel  gates  ;  intermediate  or 


86     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

partial  motions  of  the  piston  causes  correspondingly 
smaller  movements  of  the  gates. 

The  oil  pressure  type  of  governor  is  coming  into  greater 
use  in  American  hydraulic  plants,  as  it  has  been  found  from 
practical  experience  that  it  is  more  certain  and  positive  in 
its  operation  than  the  water  pressure  type,  owing  to  the  fact 
that  it  is  extremely  difficult  to  prevent  grit,  sediment,  or 
other  organic  matter  from  entering  the  governor  supply  pipe, 
thereby  clogging  up  and  hindering  the  quick  operation  of 
its  mechanism. 

The  frequent  cleanings  thus  required  in  some  cases  render 
the  use  of  the  oil  pump  far  more  satisfactory,  notwithstand- 
ing it  is  troublesome  to  maintain. 

The  type  "L"  Lombard  water  pressure  governor  shown 
in  Fig.  36  is  primarily  designed  to  regulate  large  tangential 
water  wheels,  but  is  also  applied  to  the  regulation  of  tur- 
bines of  moderate  size  under  high  head. 

The  general  construction  of  the  governor  can  be  clearly 
seen  in  the  illustration.  The  terminal  shaft  in  this  type 
makes  1.52  revolutions  to  open  the  water  wheel  gates  and 
rotates  clockwise  to  open  them. 

As  in  the  oil  pressure  type,  the  small  hand  wheel  actuates 
a  pin  clutch,  which  permits  of  the  operation  of  the  water 
wheel  gates  by  means  of  the  hand  wheel  if  desired. 

The  piston  is  terminated  in  a  rack  which  rotates  a  gear 
sector,  the  central  shaft  of  which  is  geared  or  coupled 
directly  to  the  rock  shaft  which  controls  the  deflecting 
nozzle. 

As  the  piston  travels  in  or  out  the  nozzle  deflects  the 
water  on  to  or  off  from  the  water  wheel,  or  opens  or  closes 
the  gates  of  the  turbine,  as  may  be  the  case  to  which  the 
governor  is  applied. 


HYDRAULIC   MACHINES 


F.g.  37.     Type  N,  Lombard  Water  Wheel  Governor 

Some  American  water  wheel  governors  embody  the  relay 
principle  of  operation,  which  permits  the  governed  unit  to  run 
at  a  slower  speed  when  loaded  than  when  running  empty. 


88     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  object  of  this  is  to  gradually  and  systematically  use  the 
stored  energy  in  the  rotating  parts  of  the  hydraulic  motor. 

The  Lombard  Type  "  N  "  oil  pressure  governor  shown 
in  Fig.  37  is  equipped  with  the  relaying  valve  mechanism 
and  is  especially  adapted  to  the  requirements  of  large 
water  wheel  units.  One  large  casting  forms  the  main 
cylinder  and  -the  bearings  for  the  terminal  shaft.  The 
base  forms  the  lower  cylinder  head  and  the  upper  cylinder 
head  is  integral  with  the  cylinder;  the  object  of  this  con- 
struction being  to  obtain  maximum  strength  with  least 
weight  of  metal  and  to  obviate  the  possibility  of  joints 
loosening  under  the  great  stresses  involved.  The  linear 
motion  of  the  piston  is  transformed  by  racks  and  pinions 
to  rotary  motion  at  the  terminal  shaft.  In  order  to  reduce 
the  vertical  height  of  the  governor  and  also  to  transmit  the 
force  of  the  piston  to  the  rotating  shaft  efficiently,  double 
racks  and  pinions  are  used,  the  racks  being  connected  to 
an  equalizing  yoke,  and  the  racks  'are  placed  alongside  of 
the  cylinder  instead  of  beyond  it. 

The  steel  terminal  shaft  is  2^|  inches  in  diameter  and 
is  supported  by  bearings  on  both  sides  of  the  piston.  The 
main  piston  rod  gland  cap  is  cup-shaped  so  as  to  prevent 
leakage  over  the  machine.  The  usual  form  of  hand  wheel 
is  employed  which  is  thrown  out  of  gear  when  the  governor 
is  in  regular  operation. 

The  main  valve  of  the  governor  consists  of  a  large  double 
hollow  piston  contained  in  the  horizontal  cylindrical  case 
back  of  the  rim  of  the  hand  wheel  at  the  left  of  the  figure. 
The  valve  is  perfectly  balanced  so  as  to  require  a  very  slight 
force  to  move  it,  but  in  order  to  insure  absolute  reliability 
of  movement  hydraulic  plungers  are  also  provided.  These 
plungers  are  simultaneously  actuated  by  a  small  primary 


HYDRAULIC    MACHINES 


89 


valve  secured  to  the  stem  of  the  centrifugal  balls,  and  a 
small  valveless  displacement  pump  in  the  slender  vertical 
cylinder  at  the  left  of  the  illustration  (Fig.  37).  The  piston 


Fig.  38.    Duplex  or  Differential  Relay  Governor 

of  this  pump  is  attached  to  and  moves  with  the  main  piston 
of  the  governor.     These  parts  are  so  disposed  with  respect 


QO     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

to  each  other  that  the  slightest  displacement  of  the  primary 
valve  by  the  centrifugal  balls  causes  an  instantaneous  and 
positive  movement  of  the  large  main  valve.  The  main  valve  is 
instantly  restored  to  its  closed  position  by  the  action  of  the  dis- 
placement pump  as  soon  as  the  primary  valve  is  again  closed. 
The  movement  of  the  primary  valve  results  in  an  instanta- 
neous magnification  and  insures  accurate  speed  regulation. 


Fig.  39.    A  Relay  Returning  Governor 

The  working  fluid  for  this  governor  is  a  special  oil  kept  un- 
der pressure  in  a  vertical  draw  steel  tank.  Oil  is  forced  into 
this  tank  by  a  powerful  pump  which  is  an  accessory  of  the 
governor.  The  normal  pressure  under  which  the  governor 
works  is  200  pounds  per  square  inch,  at  which  pressure  it 
exerts  the  powerful  force  of  31,000  foot-pounds  per  stroke. 


HYDRAULIC    MACHINES 


A  duplex  relay  governor  made  by  the  Replogle  Gover- 
nor Works  is  shown  in  Fig.  38.  The  operation  of  this 
governor  is  on  the  principle  that  a  movement  of  the  gate 
automatically  cuts  the  governor  out  of  action,  to  obviate 
racing  or  hunting  when  the  load  is  varied.  Or  stated 
otherwise,  there  is  a  rapid  movement  of  the  wheel  gates 
to  correspond  with  the  variation  in  load  at  the  time  of  its 
variation ;  the  gate 
movement  being  ar- 
rested in  time  to 
permit  gravitation  to 
correct  momentum 
and  inertia  effects. 
It  is  claimed  that  this 
governor  is  geared 
to  swing  a  gate 
completely  in  from 
15  to  25  seconds. 

A  relay  returning 
governor,  made  by 
the  Replogle  Com- 
pany, is  shown  in 
Fig.  39.  The  re- 
turning principle 

when  added  to  the  relay  governor  is  claimed  to  restore 
the  speed  always  to  normal,  leaving  it  identical  with  the 
speed  at  no  load. 

A  type  of  governor  of  the  hydraulic  class,  made 
by  the  Sturgess  Governor  Engineering  Company,  is 
shown  in  Fig.  40.  This  form  is  designated  type  "A," 
and  is  designed  for  operation  by  oil  pressure.  The  main 
elements  of  the  governor  consists  of  (i)  a  shaft  and 


Fig.  40.    Sturgess  Oil  Pressure  Governor 


92     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

piston  working  in  an  hydraulic  cylinder  and  actuating 
the  gate;  (2)  a  main  valve,  hydraulically  operated,  for 
admitting  pressure  to  the  hydraulic  cylinder;  (3)  a  cen- 
trifugal governor  for  controlling  the  motions  of  the 
main  valve ;  (4)  a  secondary  controller  for  gauging  the 
amount  of  gate  movement  for  any  given  variation  in 
load.  The  governor  here  shown  has  a  power  factor  of 
35,000  pounds,  and  is  designed  for  units  above  2,000 
horse-power. 

Lyndon  "Rapid"  Water  Wheel  Governor.  —  A  water 
wheel  governor  which  embodies  some  novel  features  has 
recently  been  invented  by  Mr.  Lamar  Lyndon.  This 
machine  is  claimed  to  give  very  close  regulation  in 
ordinary  power  plants  where  economy  of  water  is  im- 
portant ;  and  in  such  plants  where  the  flow  of  water 
exceeds  the  amount  of  water  used  in  the  water  wheels, 
regulation  approaching  that  of  high-speed  engines  is  said 
to  be  possible. 

The  governor  is  of  the  electrical  type  and  consists  essen- 
tially of  a  solenoid  controller  with  an  electrical  contacting 
device  which  energizes  magnetic  clutches  ;  a  small  dynamo  ; 
a  compensating  valve  ;  a  manually  operated  speed  changer; 
and  an  arrangement  of  resistances  which  prevent  over-run- 
ning of  the  gates. 

The  compensating  device  is  a  simple  butterfly  valve 
working  in  a  by-pass  pipe  which  is  tapped  into  the  flume 
or  penstock  of  the  hydraulic  machine.  Its  location  and 
operation  are  indicated  in  Fig.  41.  As  is  obvious,  all  water 
by-passed  through  the  valve  and  auxiliary  pipe  goes  around 
the  turbine  and  does  no  work. 

In  such  plants  where  the  quantity  of  water  exceeds  that 
admitted  to  the  turbines,  the  compensating  valve  is  adjusted 


HYDRAULIC    MACHINES 


93 


to  half-way  position  and  a  continual  flow  through  it  results. 
Increase  of  load  on  the  turbine,  which  causes  the  turbine 


Fig.  41.    Arrangement  of  Compensating  Valve,  Lyndon  Governor 

gate  to  suddenly  open,  causes  the  compensating  valve  to 
close   at    the    same   rate  of    speed   as   the   turbine   gate 


94     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

opens.  This  admits  an  increased  amount  of  water  into 
the  turbine,  without  necessitating  any  change  in  the 
velocity  of  water  in  the  feed  pipe;  which  permits  a 
very  quick  speed  regulation.  After  the  turbine  gate 
has  found  its  new  position  and  regulation  is  completed, 
the  compensating  valve  returns  slowly  to  its  normal  half- 


Fig.  42.     Side  Elevation  of  Lyndon  Governor 

way  position  while  the  velocity  of  the  column  of  water  in 
the  feed  pipe  also  changes  slowly  to  furnish  the  increased 
supply. 

Should  the  load  on  the  turbine  decrease,  and  the  gate 
thereby  suddenly  close,  the  compensating  valve  will  open, 
the  movement  occurring  inversely  to  the  movement  of  the 
main  gate.  The  outlet  for  the  water  from  the  feed  pipe 
being  increased,  a  less  amount  will  pass  to  the  water  wheel, 


HYDRAULIC    MACHINES  95 

and  therefore  the  suddenly  decreased  gate  opening  does  not 
mean  that  the  velocity  of -water  in  the  feed  pipe  is  suddenly 
arrested  and  great  pressure  set  up.  The  velocity  and 
pressure  remain  practically  unchanged. 

In  such  plants  where  all  the  available  water  must  be 
converted  into  work,  this  governor  will  not  afford  so  accu- 
rate regulation  but  will  give  a  very  uniform  speed.  When 
used  in  such  plants  the  compensating  valve  is  normally 
fully  closed. 

A  side  elevation  of  the  Lyndon  Governor  is  shown  in 
Fig.  42.  Fig.  43  is  a  diagrammatic  representation  of  the 
parts  and  connections.  It  consists  of  a  shaft  G  driven 
from  the  turbine  to  be  controlled.  Keyed  on  it  are  two 
iron  plates  E  and  F,  which  rotate  with  the  shaft  and  mag- 
netically are  clutched  with  plates  30  and  31  respectively. 
The  plates  30  and  31  are  secured  to  miter  gears  B  and  C 
respectively,  which  are  also  loose  on  the  shaft.  When 
either  electric  clutch  is  energized,  the  miter  gear  connected 
to  the  clutch  plate  will  turn  with  the  shaft.  Meshing  with 
the  miter  gears  B  and  C  is  a  third  gear  D,  which  is  keyed 
on  to  shaft  H,  turning  at  right  angles  to  shaft  G.  If 
clutch  plate  30  is  energized,  shaft  H  will  be  caused  to 
rotate  in  one  direction  by  the  gear  B,  while  if  clutch  plate 
3 1  be  energized,  the  shaft  H  will  be  made  to  rotate  in  an 
opposite  direction  by  gear  C. 

On  shaft  //is  mounted  a  worm  K,  which  meshes  with  a 
worm  wheel  L,  the  latter  being  mounted  on  a  third  shaft  M, 
which  is  parallel  to  shaft  G.  This  shaft  M  is  the  gate  shaft, 
and  any  movement  of  it  will  cause  opening  or  closing  of  the 
water  wheel  gate. 

It  is  obvious  that  the  gate  will  be  opened  or  closed 
according  to  whether  E  or  Fis  energized.  On  shaft  M  is 


96     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


HYDRAULIC    MACHINES  97 

a  third  magnetic  clutch  consisting  of  the  plates  A'' and  32, 
N  being  a  sheave  wheel,  having  two  grooves  in  it  in  which 
lie  the  wire  ropes  28,  29.  These  ropes  are  attached  to  the 
compensating  valve.  When  the  clutch  N  is  energized,  32 
will  be  caused  to  rotate  in  one  direction  or  the  other  accord- 
ing to  the  direction  of  motion  of  the  gate  shafts,  while  the 
ropes  will  move  the  compensating  valve  in  one  direction  or 
the  other  at  the  same  time  that  the  gates  are  moved. 

Passing  over  the  hub  of  N  is  a  heavy  leather  strap  33 
which  has  its  lower  ends  attached  to  spring  34.  Obviously 
this  spring  is  extended  whenever  N  rotates  in  either  direc- 
tion (rotation  is  limited  to  about  80  degrees). 

The  small  dynamo  which  supplies  the  energizing  current  is 
driven  from  the  shaft  G  by  means  of  gears,  and  therefore 
varies  its  speed  with  that  of  the  water  wheel.  It  is  shunt 
wound  with  laminated  fields  and  the  magnetic  density  is 
low  ;  therefore  the  voltage  will  vary  as  the  square  of  the 
speed. 

The  controller  consists  of  a  plain  solenoid  W  which  is 
connected  with  the  dynamo  having  inside  it  an  iron  core  X. 
The  passage  of  current  through  the  solenoid  tends  to  draw 
down  the  core,  such  pull  varying  as  the  square  of  the 
voltage.  Since  the  voltage  varies  as  the  square  of  the 
speed,  the  pull  on  the  solenoid  will  vary  with  the  fourth 
power  of  the  speed. 

The  governor  is  electrically  operated  in  the  following 
manner.  Referring  to  Fig.  43,  when  the  speed  is  normal 
the  lever  23  is  in  a  horizontal  position,  none  of  the  contacts 
touching  the  mercury  in  the  cups  except  point  22,  which  is 
longer  than  the  others.  When  the  core  is  pulled  down  by 
increase  of  voltage,  contacts  13  and  15  will  connect  the 
dynamo  circuit  with  clutch  30  which  will  cause  the  gate 


98     LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

shaft  to  move  in  a  direction  to  close  the  gate.  At  the 
same  time  clutch  32  will  be  connected  to  the  dynamo  circuit 
by  contacts  14  and  16  and  the  sheave  wheel  will  also  turn 
with  the  gate  shaft. 

If  a  drop  in  voltage  occurs,  causing  the  core  to  rise,  the 
gate  opening  clutch  will  be  energized  by  contacts  18  and  20, 
while  the  sheave  wheel  will  turn  in  a  direction  opposite  to 
that  in  which  it  rotates  when  the  gate  closes,  its  clutch 
now  being  energized  by  contacts  17  and  19.  Thus  the 
compensating  valve  is  always  moved  in  its  proper  direction 
whenever  the  main  gate  is  moved. 

When  governing  is  completed  and  the  speed  becomes 
normal,  the  lever  23  takes  a  horizontal  position,  thereby 
opening  the  clutch  circuits,  and  the  compensator  sheave  N 
is  drawn  by  the  spring  34  back  to  its  normal  position.  The 
water  flowing  through  and  surrounding  the  valve  gives  a 
dash  pot  action  and  makes  this  return  movement  take 
place  slowly.  Contacts  21  and  22  change  the  amount  of 
resistance  in  the  dynamo  field  with  movement  of  lever  23 
and  thereby  tend  to  restore  the  dynamo  voltage  to  normal 
before  the  dynamo  speed  has  come  to  its  proper  value ;  and 
this  arrangement  prevents  "overrunning"  or  " hitching" 
of  the  gates.  Since  the  gate  movement  in  this  type  of 
governor  takes  place  quickly,  these  machines  are  made 
very  heavy  and  powerful. 

Testing  of  Turbines  and  Water  Wheels.  —  The  data 
on  the  output,  efficiency,  and  behavior  of  their  wheels  are 
usually  obtained  by  makers  of  hydraulic  machines  from 
tests  conducted  at  the  Holyoke  testing  flumes.  As  it  is 
generally  too  expensive  for  the  purchaser  of  a  wheel  to  fit 
up  the  necessary  apparatus  for  checking  up  the  manufac- 
turer's data,  it  is  often  specified  in  the  contract  that  the 


HYDRAULIC    MACHINES  99 

wheel  be  sent  to  a  place  where  all  the  special  facilities  for 
the  test  are  available.  The  purposes  of  the  tests  are  usu- 
ally the  determination  of  effective  energy  and  power  of  the 
wheel ;  the  determination  of  efficiency  ;  the  determination 
of  the  speed  which  gives  the  maximum  power  and  effi- 
ciency. 

The  wheel  is  mounted  in  the  testing  flume,  and  run  at 
different  speeds,  in  order  to  ascertain  the  speed  which  gives 
the  maximum  efficiency  and  also  the  effective  power  output 
at  each  speed.  Since  the  efficiency  of  hydraulic  machines 
varies  appreciably  with  the  position  of  the  gate,  tests  are 
conducted  with  the  water  gate  completely  opened,  as  well 
as  at  various  intermediate  positions. 

Such  tests  afford  the  necessary  information  as  to  effec- 
tive power  and  efficiency  under  various  conditions  of  oper- 
ation, and  also  the  consumption  of  water  under  different 
heads.  The  measurement  of  effective  power  is  usually 
made  by  means  of  a  Prony  brake,  but  is  sometimes  deter- 
mined by  coupling  the  wheel  to  an  electric  generator  and 
absorbing  the  power  in  a  water  rheostat. 

Although  the  tests  at  the  Holyoke  flumes  are  accurately 
made,  they  may  be  quite  untrustworthy  to  the  turbine  user, 
since  the  data  obtained  at  the  standard  flume  may  be  con- 
siderably altered  under  different  conditions  of  wheel  set- 
tings, flumes,  and  chamber  proportions.  Thus,  the  actual 
working  conditions  to  which  the  user  must  adapt  his  wheel 
often  cause  the  machine  to  fall  short  considerably  of  con- 
firming the  manufacturer's  data. 

Faults  of  Turbines  and  Water  Wheels. — The  principal 
faults  of  hydraulic  machines  are  those  in  design  and  con- 
struction, and  such  faults  as  arise  from  bad  settings  and 
improper  wheel  cases.  The  result  of  such  errors  is  a 


100      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

machine  of  low  efficiency  and  short  life,  as  well  as  abnor- 
mal cost  of  maintenance.  Until  recently  the  turbine  was 
not  regarded  as  a  machine  of  the  highest  importance;  hence 
its  design  has  been  badly  neglected  and  nicety  of  construc- 
tive details  disregarded.  Moreover,  the  material  and  work- 
manship were,  and  are  still  in  many  cases,  of  a  very  low 


Fig.  44.    Pelton  Wheel,  Showing  Bucket  Construction 

grade.     Improvements  in  efficiency  and  in  the  design  of 
turbine  settings  still  leave  much  to  be  desired. 

Types  of  American  Water  Wheels.  —  The  Pelton  water 
wheel  shown  in  Fig.  44  is  of  the  impulse  type,  and  operates 
by  direct  pressure.  It  is  constructed  in  its  simplest  form 
of  a  cast  iron  or  steel  center,  to  the  periphery  of  which  are 
attached  tangential  vanes  or  buckets.  The  illustration 


HYDRAULIC    MACHINES  IOI 

shows  the  standard  type  wheel  mounted  in  a  wooden  frame, 
and  clearly  shows  the  bucket  construction,  the  nozzle,  and 
gate  valve.  The  buckets  are  constructed  of  steel,  phos- 
phor bronze,  or  cast  iron,  as  the  conditions  may  require. 
The  wheel  centers  are  made  of  steel  and  cast  iron,  and  for 
very  high  powers  are  of  the  disc  type.  The  wheels  are 
driven  on  the  shaft  by  hydraulic  pressure  and  rigidly 
keyed.  Bearings  are  of  the  ring-oiling  type,  the  barrels 
being  lined  with  a  special  babbitt  metal. 


Fig.  45-    A  3,030  Horse-Power  Pelton  Wheel  Direct  Connected  to  Generator 

The  housings  of  the  wheel  are  usually  constructed  of 
sheet  steel  or  cast  iron,  riveted  and  caulked,  and  have  cast 
iron  planed  flanges  for  joints.  In  order  to  prevent  leakage 
of  water  along  the  shaft  and  into  the  journals,  a  device 
known  as  a  "centrifugal  disc  "  is  employed.  It  consists  of 
a  cast  iron  disc  attached  to  the  shaft  of  the  wheel  and 
revolving  within  the  wall  chambers,  being  secured  to  the 
interior  of  the  wheel  housing.  Water  collecting  on  the 


IO2       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


shaft  is  caught  by  the  disc  and  thrown  into  the  centrifugal 
chamber,  from  which  it  is  drained  away  through  a  tube  into 
the  tail  race. 

The  Pelton  wheel  is  also  designed  for  several  nozzles,  in 
order  to  increase  the  power  of  the  wheel  without  propor- 
tionately increasing  its  diameter.  The  wheel  is  constructed 
with  a  free  discharge,  in  order  to  prevent  leaves,  trash,  or 

matter   in    suspension   from 
choking  up  the  buckets. 

Fig.  45  shows  a  3,000 
horse-power  Pelton  wheel  of 
the  iron-mounted  type,  direct 
connected  to  a  1,500  kilo- 
watt generator  through  a 
leather  link  coupling. 

The  runner  of  the  Risdon 
wheel  made  by  the  Risdon 
Iron  Works,  San  Francisco, 
is  shown  in  Fig.  46,  which 
also  shows  the  bucket  con- 
struction employed.  The 
vanes  are  of  the  tangential 
form,  and  designed  to  pre- 
vent the  water  from  reacting 
from  a  bucket  in  a  way 

which  will  cause  it  to  strike  against  a  succeeding  bucket. 
The  water  is  thus  deflected  in  a  clear  and  free  direction. 
The  buckets  are  made  interchangeable,  and  are  bolted  to 
the  rim  or  center  by  heavy,  square-headed  bolts  with  lock 
nuts  ;  each  bucket  bolting  closely  with  dovetails  to  the  one 
on  each  side  of  it,  thus  making  a  continuous  ring  when 
all  are  placed  in  position.  Buckets  of  different  size  may 


Fig.  46.    Bucket  Construction  of 
Risdon  Wheel 


HYDRAULIC    MACHINES  IO3 

be  adapted  to  conform  with  nearly  every  size  or  diameter 
of  wheel,  so  that  the  proportion  of  revolutions  to  power 
may  be  designed  to  suit  various  conditions  of  operation. 

Fig.  47  illustrates  a  3,000  horse-power,  double  unit  Ris- 
don  wheel  for  direct  connection  to  an  electric  generator. 
The  unit  consists  of  two  wheels  of  disc  form,  eight  and  a 
half  feet  in  diameter,  mounted  on  the  same  shaft,  each 
wheel  being  driven  by  a  single  jet,  at  240  revolutions  per 
minute.  The  buckets  and  centers  of  the  wheels  are  made 
of  cast  steel.  Bucket  wings  are  milled  out  on  an  Ingersoll 


Fig.  47.    Double  Unit  3,000  Horse-Power  Risdon  Wheel 

slabbing  machine,  and  driven  on  the  edge  of  the  turned 
disc.  Through  wings  and  disc,  holes  are  drilled  to  tem- 
plate, and  fitted  with  driven-in,  turned  steel  forged  bolts. 

Under  normal  load  the  bolts  securing  the  buckets  to  the 
periphery  of  the  wheel  may  be  under  a  strain  of  65,000 
pounds  each.  To  obviate  any  danger  from  this  source,  it  is 
claimed  that  the  bolts  are  each  made  to  undergo  a  strain  of 
700,000  pounds  without  breaking,  or  at  normal  load,  the 
bolts  have  the  exceedingly  high  factor  of  safety  of  sixty. 
The  discs  on  which  the  buckets  are  mounted  are  bored 


104       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


Fig.  48.     Bucket  Construction  of  the  Doble  Wheel 


and  shrunk  on  a  heavy  shaft,  the  factor  of   safety  of  which 

against  torque  and  weight  is  claimed  to  be  over  fifteen. 
The  bearings  are  of  the  adjustable,  ring- oiling  ball  and 

socket  type,  with  very  large  surfaces,  which  are  lined  with 

anti-friction  metal. 

The  Doble  Water 
Wheel.— The  Doble 
wheel,  made  by  the 
Abner  Doble  Com- 
pany, of  San  Fran- 
cisco, is  also  of  the 
tangential  ellipsoidal 
type.  Fig.  48  shows 
the  bucket  construc- 
tion of  the  wheel, 
and  Fig.  49  shows 
the  runner  of  a  3,700 

horse-power    wheel  designed  for  operation  under  a  head 

of  1,531  feet.     The 

wheel    proper   or 

body  is  constructed 

of    a     nickel    steel 

forging,    10   feet    5 

inches  in  diameter, 

and  weighing    over 

io,ooopounds.   The 

buckets    are    made 

of  open-hearth  steel 

castings,     and    are 

designed    for   a   jet 

of  water   four  and  a  half  inches  in  diameter.      Each  bucket 

is  fastened  to  the  periphery  of  the  wheel  by  two   fitted 

bolts  in   reamed  holes. 


Fig.  49.    Runner  of  3,700  Horse-Power  Doble  Wheel 


HYDRAULIC   MACHINES 


105 


Fig.  50.    Needle-Regulating  Nozzle 


The  nozzle  used  on  the  Doble  wheel  is  of  the 
needle-regulating  type;  the  adjustment  being  effected 
by  moving  a  core 
axially  within  the 
nozzle,  thereby  vary- 
ing the  annular  area 
of  the  orifice.  Fig. 
50  shows  a  jet  issu- 
ing from  a  needle- 
regulating  nozzle  under 
a  high  head. 

Accessories  of  Tur- 
bines and  Water 
Wheels.  —  In  regulat- 
ing the  supply  of  water  to  a  hydraulic  machine  a  gate 

valve  or  several  gate  valves 
are  used.  Such  valves  are 
arranged  to  work  in  a  ver- 
tical plane  by  partially  or 
entirely  closing  the  admis- 
sion orifice  through  the  me- 
dium of  a  hand  wheel  or 
by  means  of  gearing  or  rig- 
ging operated  electrically  or 
hydraulically. 

Various  forms  of  gate 
valves  are  in  use  in  Amer- 
ican hydro-electric  plants. 
Fig.  51  shows  the  Pelton 
gate  valve.  It  belongs  to 
the  straight-way  single  disc 
type  of  valve,  and  is  designed  for  pressure  on  one  side 


Fig.  51.    A  Straight-way  Single 
Disc  Gate-Valve 


IO6      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

only.  The  spindle  of  the  valve  can  be  so  manipulated 
by  means  of  the  hand  wheel  as  to  bring  the  disc  entirely 
clear  of  the  opening,  thus  allowing  free  passage-way  for 
the  water.  When  the  valve  is  used  on  pipe  systems  in 
which  the  pressure  is  very  high  it  is  fitted  with  ball- 
bearings or  some  form  of  gearing. 


Fig.  52.     Battery  of  Relief  Valves  for 
High-Pressure  Pipe  Lines 


Fig.  53.    The  Lombard  Water- 
Balanced  Relief  Valve 


Safety  Relief  Valves  become  necessary  on  pipe  or  con- 
duit systems  working  under  very  high  pressure.  They 
are  generally  placed  at  the  lower  end  of  the  pipe  line,  in 
close  proximity  to  the  nozzle.  Their  operating  pressure 
slightly  exceeds  the  normal  working  pressure,  and  in  case 
of  a  sudden  stopping  of  the  water  flow  by  the  closure  of 
the  gate  valve  or  some  accident  to  the  governor,  the  safety 
valves  open  for  an  instant  to  relieve  the  pressure.  This 
safeguards  the  pipe  system  against  the  serious  dangers 


HYDRAULIC    MACHINES 


ID/ 


resulting  from  water  hammer.  If  the  pipe  line  is  of  very 
large  size  and  the  pressure  extremely  high,  a  battery  of 
safety  relief  valves  is  used.  Fig.  52  shows  a  battery  of 
such  valves,  made  by  the  Pelton  Wheel  Company. 

Fig.  53  shows  the  Lombard  water-balanced  relief  valve. 
In  this  type  of  safeguarding  appliance  the  pressure  of  the 
water  against  the  gate  valve 
is  opposed  by  the  hydrostatic 
pressure  at  the  point  where 
the  valve  is  fitted  to  the  flume 
or  casing  of  the  wheel.  The 
valve  remains  closed  so  long 
as  the  operating  pressure  does 
not  exceed  the  static  pressure. 
But  when  the  normal  pressure 
is  exceeded  in  the  flume  the 
valve  at  once  opens  and  dis- 
charges water  until  the  press- 
ure is  restored  to  the  normal 
condition. 

Fig.  54  shows  a  Ludlow 
high-pressure  valve  of  the 
double-gate  type,  constructed 
of  iron  and  bronze.  The  valve 
is  operated  by  means  of  bevel 
gearing,  the  position  of  the' 
gates  being  adjustable  with 
center  bearings  to  prevent  the  sticking  of  the  parts. 
The  type  shown  is  fitted  with  an  indicating  device  to 
show  the  position  of  the  gate,  and  also  a  by-pass  outlet. 


Fig.  54.     Mechanically  Operated 
Gate  Valve 


108      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


BIBLIOGRAPHY 

Mechanics  of  Engineering.     Volume  2.     Hydraulics  and   Hydraulic 
Motors.     Weisbach-Du  Bois. 

The  Theory  of  Impulse  Wheels.      Kingsford.     Engineering    News. 
July  21,  1898. 

Turbines.     Wood.    Second  Edition.    Wiley  &  Sons.    New  York.    1901. 

The    Need    of    Turbine    Standards    of    Measurement.      Replogle. 
Engineering  News.     October  23,  1902.      Page  339. 

Water-Wheel    Regulation.      Garrett.       Gassier* s     Magazine.       New 
York.     May,  1901. 

Report    of   a   Turbine    Test.      Webber.      Engineering  News.     New 
York.     April  20,  1903.      Page  386. 

Tangential  Water- Wheel  Efficiencies.     Henry.     Transactions  Pacific 
Coast  Electric  Transmission  Association.     June  16,  1903. 

Modern  Turbine  Practice  and  Water-Power  Plants.    Thurso.    D.  Van 
Nostrand  Company,  New  York.     1906. 


CHAPTER    IV 

GENERATORS,   SWITCHES,   AND   PROTECTIVE 
DEVICES 

Kinds  of  Generators  Used.  —  Three  distinct  types  of 
alternating-current  machines  are  used  in  generating  current 
for  long-distance  transmission,  namely,  the  revolving  arma- 
ture generator,  the  revolving  field  generator,  and  the 
inductor  generator.  Of  these  types  the  revolving  field 
generator  is  most  used,  and  is  rapidly  supplanting  the 
other  two  types. 

The  revolving  armature  alternator  is  generally  used  in 
outputs  up  to  800  kilowatts.  The  field  magnet  of  this 
type  of  machine  is  constructed  of  either  laminated  or  solid 
steel,  either  cast  into  the  frame  of  the  machine  or  bolted 
to  it  radially.  In  some  few  cases  cast-iron  poles  are  used. 
The  magnet  coils  are  in  nearly  every  case  form  wound  on 
collapsible  mandrels,  and  the  conductor  is  copper  wire,  bar, 
or  strap,  depending  on  the  output  of  the  machine.  Field 
magnet  coils  are  insulated  with  oiled  muslin  or  linen, 
fuller  board,  micabeston,  vulcabeston,  etc.,  and  the  sepa- 
rate layers  are  sometimes  protected  by  coatings  of 
shellac. 

The  armature  of  this  type  of  generator  is  generally 
drum  or  barrel  wound,  and  the  core  is  usually  of  the 
toothed  type.  The  armature  coils  are  almost  invariably 
form  wound  and  of  substantially  rectangular  outline  ;  in 
machines  of  considerable  output  the  conductors  are  copper 

109 


110      LONG-DISTANCE  ELECTRIC   POWER  TRANSMISSION 

straps  or  bars,  each  insulated  from  its  neighbor  by  layers 
of  fiber  impregnated  with  a  bituminous  compound  and 
varnished  with  a  heavy  coating  of  shellac,  or  by  micanite 
and  oiled  linen,  or  some  similar  combination. 

The  separate  conductors  belonging  in  one  slot  are  assem- 
bled into  a  bundle  and  tightly  bound  together  with  insu- 
lating tape  coated  with  a  moisture-proof  compound.  The 
bundles  of  bars  are  then  laid  in  the  slots  around  the  pe- 
riphery of  the  armature  coils,  which  are  insulated  by  troughs 
of  insulating  material ;  after  the  coils  are  secured  in  place 
they  are  connected  up  to  each  other  and  the  complete 
winding  is  connected  to  the  "  collector  rings." 

The  revolving  field  generator  is  built  in  two  general 
forms :  one  in  which  the  field  magnet  surrounds  the  arma- 
ture, as  in  the  case  of  the  Niagara  Falls  machines,  and  the 
other  in  which  the  armature  surrounds  the  field  magnet ; 
the  latter  is  the  more  generally  used.  External  field  ma- 
chines with  revolving  magnets  are  used  only  in  special 
work,  such  as  that  at  Niagara  Falls.  In  construction  they 
are  generally  similar  to  revolving  armature  machines, 
except  that  the  shaft  is  usually  vertical,  for  coupling  to  a 
water  turbine,  and  the  field  magnet  is  of  the  overhung  or 
umbrella  type. 

The  revolving  field  generator  with  the  armature  sur- 
rounding the  field  magnet  comprises  an  annular  armature 
core,  mounted  in  a  cast-iron  housing,  and  a  wheel  or 
spider  mounted  on  the  shaft  and  carrying  radial  field  mag- 
net poles  on  its  periphery.  The  armature  winding  is  laid 
in  slots  around  the  inside  of  the  armature  core.  In  machines 
of  large  output  this  mode  of  construction  has  much  to 
recommend  it,  its  especial  advantage  being  that  with  a 
given  peripheral  speed  of  the  moving  element  there  is  more 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES     I  I  I 

room  for  the  disposition  of  the  armature  coils.  More- 
over, since  the  coils  are  stationary,  they  admit  of  a 
higher  degree  of  insulation  than  is  possible  with  moving 
windings. 

The  frame  of  the  revolving  field  type  being  provided 
with  air  ducts,  the  rotating  field  maintains  a  better  circula- 
tion of  air  through  the  coils  than  is  the  case  with  the 
stationary  field  type»  The  absence  of  moving  contacts  for 
taking  off  currents  of  large  value  is  also  highly  advan- 
tageous. The  only  moving  terminals  are  those  for  estab- 
lishing connection  with  the  field  winding,  and  which  have 
to  carry  but  small  currents  at  low  voltages. 

The  Inductor  Generator.  —  In  this  type  both  field  and 
armature  windings  are  stationary,  the  rotating  member  con- 
sisting of  bare,  soft  iron  fitted  with  projections  termed  "in- 
ductors." The  projections  receive  their  magnetization  from 
an  annular  field  coil,  which  also  magnetizes  the  stationary 
part  of  the  magnetic  circuit.  The  frame  surrounding  the 
inductor  has  radial  projections  which  correspond  to  the 
inductors  both  in  number  and  proportions,  and  on  these 
are  mounted  the  generating  coils.  (See  Figs.  $6a  and  56^.) 

When  the  inductors  in  rotation  come  immediately  op- 
posite to  the  faces  of  the  stationary  poles,  the  magnetic  re- 
luctance is  at  its  lowest  value,  consequently  the  flux  through 
the  generating  coils  is  at  its  maximum  value.  Conversely, 
when  the  inductors  are  at  intermediate  positions,  the  mag- 
netic flux  interlinked  with  the  generator  coils  is  smallest, 
and  consequently  the  E.M.F.  is  at  its  lowest  value. 

Hence,  at  the  various  polar  points  around  the  frame  of 
the  generator  the  flux  is  varying  from  maximum  to  mini- 
mum, and  back  again,  but  does  not  alter  its  direction  or 
polarity. 


112       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Inductor  generators  are  wound  to  deliver  single  and  poly- 
phase currents,  the  armature  windings  being  usually  of  the 
concentrated  type.  It  will  be  apparent  from  the  shape  of 
the  pole  pieces  that  the  instantaneous  value  of  the  E.M.F. 
in  a  coil  is  proportional  to  the  strength  of  the  magnetic 
field  which  it  is  cutting  at  that  instant.  Hence,  with  a 
fairly  uniform  magnetic  density  over  the  pole  face,  the  curve 
of  instantaneous  E.M.F.  during  a  cycle  will  not  be  a  sine 
curve,  but  a  flat-topped  curve  with  an  abrupt  approach  to 
a  zero  value. 

An  approximate  sine  curve  in  an  inductor  generator  may 
be  obtained  by  a  distribution  of  the  windings  in  two  or 
more  slots  per  pole  per  phase,  or  else  by  such  shaping 
of  the  pole  faces  as  will  vary  the  density  in  the  air  gap, 
so  as  to  carry  the  E.M.F.  wave  up  gradually  instead  of 
suddenly. 

Since  all  the  poles  on  one  side  of  the  inductor  generator 
have  the  same  polarity,  the  magnetization  of  the  armature 
teeth  and  iron  is  approximately  in  the  same  direction. 

The  advantages  claimed  for  the  inductor  generator  are, 
that  the  iron  is  worked  through  only  half  a  cycle,  which 
makes  the  iron  losses  quite  small,  if  the  machine  is  worked 
at  low  magnetic  densities  ;  freedom  from  moving  wire,  which 
reduces  the  liability  to  breakdown  by  the  chafing  of  insu- 
lation ;  ample  space  for  insulation,  due  to  stationary  wire  ; 
absence  of  moving  current-collecting  devices,  and  hence  no 
losses  due  to  sparking  and  brush  friction. 

The  Regulation  of  Generators.  —  The  inherent  regulation 
of  an  alternating-current  generator  is  usually  defined  as  the 
percentage  rise  of  voltage  when  the  total  non-inductive 
load  is  thrown  off,  both  generator  speed  and  field  excita- 
tion being  kept  constant. 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      113 

According  to  the  Standardization  Committee  of  the 
American  Institute  of  Electrical  Engineers,  "The  regu- 
lation of  an  apparatus  intended  for  the  generation  of 
a  potential,  current,  speed,  etc.,  varying  in  a  definite 
manner  between  full  load  and  no  load,  is  to  be  measured 
by  the  maximum  variation  of  potential,  current,  speed, 
etc.,  from  the  satisfied  condition  under  such  constant 
conditions  of  operation  as  give  the  required  full  load 
values." 

In  apparatus  which  transforms,  generates,  or  transmits 
alternating  currents,  regulation  refers  to  non-inductive  load, 
i.e.,  load  in  which  the  current  is  in  phase  with  the  E.M.F. 
at  the  outside  of  the  apparatus,  and  is  expressed  in  per- 
centage of  the  full  load  value. 

The  inherent  regulation  of  standard  American  alter- 
nators varies  from  sixteen  per  cent  to  six  per  cent  on 
non-inductive  load,  depending  on  the  output  and  type  of 
machine. 

On  inductive  load  the  regulation  of  standard  machines 
varies  from  twenty  to  ten  per  cent  according  to  the  output 
and  the  kind  of  machine. 

The  fundamental  factor  involved  in  securing  high  inher- 
ent regulation  in  a  generator  is  good  inductive  load  regu- 
lation, which  means  the  use  of  large  amounts  of  copper 
and  high  magnetic  densities  in  the  iron.  High  inherent 
regulation  is  obtained  at  the  expense  of  output  per  pound 
of  material. 

Generators  for  long-distance  power  transmission  work 
should  have  good  inherent  regulation,  because  machines 
under  such  conditions  of  operation  cannot  be  compounded, 
for  the  reason  that  compounding  would  only  compensate 
for  the  losses  at  one  definite  power  factor. 


114     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


Moreover,  in  the  majority  of  high-tension  stations  the 
machines  are  worked  in  parallel,  in  which  case  compound- 
ing becomes  impractical. 

Efficiency  of  Generators.  —  The  efficiency  of  an  alternat- 
ing-current machine  is  the  ratio  of  its  net  power  output  to 
its  gross  power  output.  The  determination  of  the  efficiency 
of  an  alternator  is  made  by  measuring  the  electric  power 
when  the  current  is  in  phase  with  the  E.M.F.,  unless 
otherwise  specified. 

In  case  a  generator  has  an  exciter  or  other  auxiliary 
apparatus  the  power  consumed  by  the  auxiliary  apparatus 
should  not  be  charged  to  the  machine,  but  to  the  entire 
plant  comprising  machine  and  auxiliaries  taken  together. 
Plant  efficiency  is  then  to  be  distinguished  from  machine 
efficiency. 

Efficiencies  of  generators  used  in  long-distance  power 
plants  vary  £rom  90  to  97.5  per  cent  (at  full  load).  Fig.  55 
shows  th(^fliJM0MB  curve,.,of  an  1^850  kilowatt  machine. 
The  table  below  gives  efficiencies  of  several  Bullock 
generators. 


LOAD. 

i 

$ 

1 

1 

H 

ii 

AK  14-9,015|,  1,000  kw.,  11,000  v.,  257  rev  
AK  18-7,517,  1,200  k\v  ,  2,300  v.,  400  rev  

86. 
87. 

92.2 
93 

94.2 
95. 

95.2 
96. 

95.7 
96.6 

96 

AI  50-180  14|,  1,500  kw.,  2,400  v.,  120  rev  
A  K  26-130-20  2  000  kw    2200  v.   231  rev. 

87.8 
87.4 

93.4 
92.9 

95. 

95. 

96. 
96. 

96.5 
96.5 

96.7 
96.9 

AI  96-36,011,  2,500  kw.,  4,500  v.,  75  rev  
"         "       3,000  k  w.,  4,500  v.,  75  rev  
AK  16-6,519,  800  kw.,  2,300  v.,  450  rev  
AK  36-l,207|,  750  kw.,  2,400  v.,  200  rev    
AH  18-7,512,  600  kw.,  2,400  v.,  400  rev  
AI  60-1,807,  400  kw.,  2,400  v.,  120  rev  

90. 
91. 

85. 
86. 
80. 
80.3 

94.2 
95. 
91.5 
92. 
89. 
88.6 

95.6 
96.2 
94. 
94.2 
92. 
91.7 

96.3 
97. 
95. 
95. 
93.5 
93.2 

96.6 
97.4 
95.5 
95.4 
94.3 
94. 

96.8 
97.6 
95.7 
95.4 
95. 
94.3 

Parallel  Operation  of  Generators.  —  The  parallel  operation 
of  generators  in  hydro-electric  plants  is  absolutely  essential 
to  economical  operation  in  cases  where  large  powers  are 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES     115 

developed,  in  order  to  reduce  the  number  of  circuits  and 
transmission  lines.  Generators  of  standard  make  and 
proper  design,  coupled  to  water  wheels,  operate  in  parallel 


1 850  K.W    1 4,500  VOLTS., 

180  REV.,28  POLES 


100      AMPERES  EXCIJATION       200 

Fig.  55 

with  absolute  reliability  and  simplicity,  because  of  the  per- 
fectly uniform  angular  motion  of  water  wheels. 

The  most  important  requirement  of  a  generator  intended 
for  parallel  operation  is  a  reasonable  amount  of  armature 
reactance.  If  the  reactance  is  too  small,  an  enormous 


Il6      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

exchange  of  current  between  the  machines  is  liable  to 
occur  when  there  is  even  a  slight  difference  in  their  field 
excitation,  or  if  the  machines  are  thrown  in  parallel  when 
there  is  a  slight  phase  difference  between  them.  Parallel 
operation  of  machines  with  an  excessive  amount  of  arma- 
ture reactance  can  also  be  effected,  but  their  operation 


Fig.  560.    Construction  of  2,000  K.  W.  Water-Wheel  Type  Inductor 
Generator 

under  such  conditions  is  not  stable,  and  "  hunting  "  fre- 
quently occurs,  due  to  the  exchange  of  a  small  synchron- 
izing current  between  them. 

In  cases  where  a  number  of  generators  are  operated  in 
parallel  the  field  excitation  of  each  machine  is  individually 
adjusted  to  enable  it  to  supply  its  share  of  the  total 


GENERATORS,    SWITCHES,    PROTECTIVE   DEVICES        I  I/ 

current,  which  prevents  an  exchange  of  current  between 
the  machines. 

The  fly-wheel  effect  obtained  from  the  large  masses  of 
metal  in  revolving  field  generators  conduces  greatly  to 
stability  of  operation  in  parallel,  and  tends  to  produce  uni- 
formity ,of  angular  motion. 

Figs.   $6a  and  56^  show   a  2,000  kilowatt    high-speed 


Fig.  566.    A  a, ooo  K.  W.  Water-Wheel  Type  Inductor  Generator  Completed 

water-wheel  type  inductor  alternator,  made  by  the  Stanley 
Electric  Manufacturing  Company.  The  stationary  part 
of  the  machine  nearest  the  air  gap  is  built  up  of  laminated 
iron,  the  coils  being  wound  and  insulated  separately  and  laid 
in  slots  in  this  part,  in  the  shape  in  which  they  are  wound. 


IlS       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  single  field  coil  is  stationary  and  is  form  wound  on 
a  brass  spool  from  which  it  is  thoroughly  insulated.  The 
secondary  action  of  the  brass  spool  tends  to  obviate  danger 
from  the  breaking  down  of  the  insulation  of  the  coil  when 
the  field  circuit  is  broken. 

The  revolving  part  consists  of  bare  cast  steel,  keyed  to 
the  shaft,  and  is  filled  with  laminated  iron  projections  or 


Fig.  57.    A  Bullock  3,000  K.  W.  Water-Wheel  Type  Generator 

inductors  on  its  surface.  The  bearings  are  of  the  self- 
oiling,  self-aligning  type- 
Fig.  57  shows  a  3,000  kilowatt,  4,400  volt,  3  phase,  60 
cycle  Bullock  revolving  field  generator  of  the  water-wheel 
type.  The  armature  is  built  up  of  mild  annealed  steel  of 
high  permeability,  the  laminae  being  japanned  to  reduce 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      I  19 

eddy  currents.  The  armature  coils  are  wound  on  cast-iron 
forms,  the  conductors  being  carefully  insulated  from  each 
other  and  from  the  core. 

The  field  coils  are  constructed  of  copper  strap  bent 
edgewise.  The  difference  of  potential  between  the  turns 
is  but  a  fraction  of  a  volt,  which  insures  freedom  from  in- 
sulation breakdown.  The  bearings  are  of  the  self-adjusting, 
self -oiling  type. 

Fig.  58  shows  a  3,750  kilowatt  water-wheel  type  Westing- 
house  revolving  field  generator.  The  illustration  shows 
the  machine  during  erection  in  a  hydro-electric  plant.  The 
field  magnet  is  constructed  of  laminated  steel  punchings 
fastened  together  by  bolts  and  dovetailed  into  a  cast-iron 
spider.  This  spider  does  not  form  a  part  of  the  magnetic 
circuit,  the  lines  of  force  going  only  through  the  lamina- 
tions. The  construction  is  designed  to  give  the  rim 
sufficient  strength  to  resist  the  strains  caused  by  cen- 
trifugal force  without  straining  the  central  spider.  The 
field  magnet  coils  are  form  wound  with  copper  strap 
bent  on  edge.  Wedges  of  copper  serve  to  retain  the 
coils  in  place  and  also  act  as  "dampers"  to  reduce  the 
shifting  of  the  flux  across  the  pole  faces  due  to  armature 
reaction. 

The  armature  is  built  up  of  slotted  steel  punchings 
dovetailed  within  a  cast-iron  frame.  The  winding  consists 
of  copper  strap  bent  into  the  required  shape  and  held  in 
open  slots  by  hard  fiber  wedges. 

Switchboards  for  High-Tension  .Current.  —  The  switch- 
board being  virtually  the  heart  of  a  transmission  system, 
its  design  and  equipment  are  of  vital  importance  in  the 
safe  and  trustworthy  operation  of  a  plant. 

Switchboards  for  high-tension  plants  are  made  of  care- 


120       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES       121 

fully  selected  marble  and  built  up  of  panels,  or  units, 
which  are  bolted  to  structural  steel  frames. 

The  majority  of  high-tension  boards  in  stations  of  large 
output  are  provided  with  a  separate  panel  for  each  gener- 
ator as  well  as  a  p'anel  for  each  exciter  unit  ;  and  in  plants 
where  two  different  pressures  are  generated  there  are  gen- 
erally panels  for  the  feeders.  A  main  junction  panel  in 
the  middle  of  the  board  is  sometimes  provided  by  means  of 
which  it  is  possible  to  divide  the  board  electrically  into  two 
parts,  either  of  which  may  be  closed  down  for  repairs 
while  the  other  is  in  service. 

A  high-tension  generator  panel  is  usually  equipped  with 
one  or  more  circuit  breakers ;  single-pole,  double-throw 
main  switches  ;  two  or  three  long-scale  alternating-current 
ammeters  ;  a  dead-beat  direct-current  ammeter  for  the  field 
circuit;  a  double-pole,  single-throw,  quick-break  field  switch, 
with  shunt  resistance  and  discharge  attachment ;  series 
and  shunt  transformers  \m  synchronizing  devices  ;  indicat- 
ing and  integrating  wattmeters,  etc. 

In  many  cases  the  rheostats  in  high-tension  stations  are 
mounted  under  the  gallery  floor  (or  the  main  floor  of  the 
station),  and  are  controlled  by  hand  wheels  on  pedestals 
located  directly  in  front  of  their  respective  generator 
panels. 

On  some  high-tension  boards  there  is  provided  a  mul- 
tiplying panel  for  duplicating  the  bus-bars.  Multiplying 
panels  are  provided  with  a  double-pole,  hand-operated 
circuit  breaker  ;  single-pole,  single-throw  multiplying 
switches  ;  a  synchronizing  device  and  double-throw  switch 
for  throwing  the  synchronizing  device  on  any  of  the  several 
sets  of  bus-bars. 

Each    panel   for   the   raising    transformers    is    usually 


122       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

equipped  with  a  single-pole  automatic  overload  circuit- 
breaker,  with  time-limit  relays ;  a  long  scale  am- 
meter ;  a  double-throw,  double-pole  main  switch ;  light- 
ning arresters  and  static  interrupters,  together  with 
various  auxiliary  devices  depending  on  the  size  of  the 
unit.  For  each  group  or  bank  of  transformers  there  is 
provided  an  integrating  wattmeter  and  several  shunt 
transformers. 

In  some  high-tension  stations  the  high  potential  board 
is  arranged  so  that  either  of  the  two  transmission  lines 
may  be  operated  on  either  bank  of  the  transformers, 
so  that  either  half  of  the  switchboard  may  be  "  dead- 
ened "  for  cleaning  or  repairs  while  the  other  is  in 
operation. 

Switches  for  Handling  High  Voltages.  —  No  apparatus 
employed  in  high-tension  electric  power  transmission  is  of 
more  vital  importance  than  the  switches  used  in  controlling 
the  circuits.  The  severe  demands  imposed  on  this  part  of 
the  electrical  equipment  necessitate  the  highest  skill  and 
familiarity  with  the  requirements  which  circuit-controlling 
appliances  must  fulfill. 

Switches  used  in  American  high-tension  practice  are  of 
several  general  types,  namely,  air-break  switches,  com- 
bined air-break  switches  and  fuses,  oil-break  switches,  com- 
bined oil-break  switches  and  circuit  breakers. 

Oil-Break  Switches.  —  For  circuits  operating  under  a 
pressure  of  a  few  thousand  up  to  60,000  volts,  the  oil- 
break  type  of  switch  has  adequately  demonstrated  its  reli- 
ability. A  type  of  oil-break  switch  extensively  used  in 
plants  of  moderate  pressure  —  i.e.,  up  to  15,000  volts  —  is 
shown  in  Fig.  59.  It  consists  of  two  or  three  double-pole 
single-phase  elements  or  switches  (the  number  depending 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      123 


on  whether  the 
circuit  is  two 
phase  or  three 
phase)  inclosed 
each  in  a  fire- 
proof cell,  but 
arranged  for 
simultane  ous 
operation.  Each 
element  of  the 
switch  is  usually 
made  up  of  two 
brass  cylinders, 
one  cylinder  per 
pole.  The  in- 
coming terminal 
of  one  phase  is 
attached  to  one 
cylinder,  and  the 
outgoing  termi- 
nal of  the  same 
phase  to  the 
other  cylinder. 
Each  cylinder  is 
filled  about  two 
thirds  full  of  oil 
and  is  covered 
over  with  a  metal 
cap,  to  which  is 
attached  a  long 
insulatingsleeve. 
Two  copper  rods  forming  vertical  spindles  and  united  by 


Fig.  59.    Oil-Break  Switch  for  Moderate  Pressures 


124       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

a  metallic  cross-head  at  the  top  slide  through  the  insulating 
sleeve  and  fit  into  tubular  contacts  at  the  bottom  of  the 
cylinder  when  operating  to  close  the  circuit.  To  the 


Fig.  60.    Type  of  Oil-Break  Switch  for  High  Pressures 

cross-head  of    the  copper  rods  is  attached  a  wooden  rod 
extending  through  the  top  of  the  cell  which  incloses  the 
switch.     This  rod   is   attached   to    a    metallic    cross-head, 
which  is  actuated  by  either  electric  or  pneumatic  devices. 
When  the  rod  conductors  of  the  switch  are  raised  the 


GENERATORS,  SWITCHES,   PROTECTIVE    DEVICES      125 

circuit  is  broken  under  the  oil  in  two  places  in  each  phase. 
The  range  through  which  the  cross-head  can  be  actuated 
varies  with  the  pressure  which  the  switch  has  to  handle. 
In  order  to  keep  the  arc  from  jumping  from  the  copper 
rod  to  the  cylinder  when  it  is  drawn  through  the  oil,  the 
cylinders  are  lined  on  the  inside  with  fiber.  The  isolation 
of  the  composite  poles  of  the  switch  in  separate  fireproof 
compartments  is  to  prevent  a  burn-out  in  one  cell  from 
spreading  to  the  others,  and  thus  causing  a  complete 
breakdown  of  the  switch. 

Another  type  of  oil  switch  in  successful  operation  on 
high-tension  circuits  is  shown  in  Fig.  60.  The  switch 
mechanism  comprises  two  or  more  metallic  contact  pieces 
depending  upon  whether  the  switch  is  of  single,  double,  or 
triple  pole  type.  The  contact  pieces  are  attached  to  sepa- 
rate rods  of  chemically  treated  wood,  which  in  turn  are 
attached  to  a  cross-head  actuated  in  a  vertical  "plane  by  a 
system  of  levers.  Each  contact  piece  makes  electric  con- 
nection by  means  of  a  clip,  which  is  supported  from  the 
frame  by  porcelain  insulators,  so  as  to  insulate  all  live 
parts.  When  the  contact  pieces  are  brought  to  their 
upper  position,  the  switch  is  closed.  On  opening,  the 
contacts  fall  into  the  bottom  of  the  oil  cylinder. 

The  live  parts  of  the  switch,  such  as  clips,  contact  pieces, 
etc.,  are  entirely  immersed  in  oil  when  the  cylinder  is  fitted 
in  place.  A  switch  of  this  type  is  not  intended  to  break 
loads  under  extreme  emergencies,  such  as  a  short  circuit 
just  beyond  the  switch  on  the  load  side.  Nor  is  its  use 
advisable  directly  on  panels  which  in  extreme  instances 
can  exceed  2,500  kilowatts,  three-phase,  or  1,500  kilowatts, 
single-phase  power.  Under  such  conditions,  single-pole, 
single-phase  switches  of  the  type  shown  in  Fig.  59  are 


126       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

generally  employed.  The  type  of  switch  here  shown  is 
automatic  in  its  operation  and  is  designed  to  perform  all 
of  the  functions  of  a  circuit  breaker.  Two  kinds  of 


Fig.  61.  Switchboard  Tripping  Mechanism  of  Oil  Switch 

mechanism  are  used  to  actuate  it,  these  differing  from 
each  other  according  to  whether  the  switch  is  mounted 
directly  on  the  switchboard  or  is  placed  in  cells  at 
some  distance  away.  The  mechanism  of  the  first  or  the 
switchboard  tripping  mechanism  is  shown  in  Fig.  61.  It 


GENERATORS,    SWITCHES,    PROTECTIVE   DEVICES      1 2/ 

is  made  up  of  a  series  of  coils  placed  on  the  face  of  the 
board  and  energizing  armatures  which  operate  to  release  a 
latch  on  the  interconnecting  link  between  switch  and 
handle.  Connected  in  series  with  the  main  switch  are  the 
secondaries  of  current  transformers  which  energize  the 
coils  of  the  tripping  device.  When  the  switch  is  auto- 
matically opened  by  this  tripping  device,  the  handle  on 


Fig.  62.    Portion  of  Circuit  Breaker  on  Face  of  Switchboard 

the  face  of  the  board  remains  closed,  and.  the  link  moves 
forward  through  the  handle,  giving  unmistakable  indica- 
tion that  the  switch  has  automatically  opened. 

Combined  Oil-Break  Switch  and  Circuit  Breaker.  —  A 
radically  different  type  of  oil-break  switch  with  attached 
circuit  breaker  is  shown  in  Figs.  62  and  63.  Fig.  63  shows 
the  portion  of  the  switch  behind  the  board.  Fig.  62  is 


128       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

an  illustration  of  the  portion  of  the  mechanism  which  is 
on  the  face  of  the  board.  Each  pole  of  the  switch  is 
immersed  in  oil  in  a  separate  compartment  lined  with 
procelain  ;  the  object  of  this  arrangement  being  the  pre- 
vention of  current  leakage  and  short  circuits  from  pole  to 


Fig.  63.    Portion  of  Circuit  Breaker  Behind  Switchboard 

pole.  Each  contact  is  tipped  with  zinc  in  order  to  obviate 
pitting  action  on  the  blades.  By  means  of  the  four 
screws  fitted  in  the  marble  cover  of  each  compartment 
of  the  switch  the  tank  may  be  removed  without  disturb- 
ing the  switch  mechanism,  even  while  it  is  carrying  current. 
This  form  of  oil  switch  is  used  in  either  the  single  or 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      1 29 

double  throw  type  with  single,  double,  triple,  or  quadruple 
poles.  Its  capacity  ranges  from  4,000  volts  and  1,000 
amperes  to  15,000  volts  and  100  amperes.  The  circuit- 
breaker  attachment  is  operated  by  means  of  the  disc 
shown  at  "the  lower  part  of  the  illustration,  Fig.  62.  The 
circuit  breaker  is  adjusted  to  open  at  different  loads  by  set- 
ting the  dial  hand  at  the  points  corresponding  to  the 
loads. 

Air-Break  Switch  with  Fuse.  —  A  very  ingenious  air- 
break  switch,  with  fuse  attachment,  is  shown  in  Fig.  64. 
This  type  of  switch  is  in  use  in  the  plants  of  the  Bay 
Counties  Power  Company  and  the  Standard  Electric  Com- 
pany, of  California,  and  deals  with  potentials  as  high  as 
60,000  volts. 

The  elements  of  the  switch  consist  of  a  main  arm,  an 
auxiliary  arm,  a  fuse  holder,  and  two  contact  pins.  The 
main  arm  consists  of  a  wooden  rod  hinged  at  the  lower 
end  to  a  bracket  mounted  on  the  switchboard.  On  the  top 
of  the  main  arm  are  mounted  two  zinc  jaws  which  hold  one 
end  of  the  fuse.  The  arm  also  carries  two  blades  which 
make  contact  with  the  terminal  jaws.  The  blade  near  the 
free  end  is  electrically  connected  to  the  zinc  jaws,  while 
the  lower  one  is  connected  by  means  of  a  cable  to  the  aux- 
iliary arm. 

The  auxiliary  arm  is  a  hollow  wooden  rod  hinged  at  its 
lower  end  to  the  main  arm. 

Attached  to  its  free  end  are  two  zinc  plates  forming 
the  holders  for  the  other  end  of  the  fuse.  A  copper  rod 
attached  to  the  auxiliary  arm  forms  the  connection  be- 
tween these  plates  and  the  cable  which  connects  the  lower 
blade  on  the  main  arm. 

In  the  event  of  the  fuse  becoming  unlatched  or  blowing' 


130      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


out,  the  auxiliary  arm  is  quickly  pulled,  the  jar  of  its  fall 
being  absorbed  by  a  dash  pot  attached  by  a  bracket  to  a 
main  arm. 

The  fuse  holder  comprises  a  hollow  insulating  tube  fitted 
at  each  end  with  perforated  corks,  and  filled  with  a  non- 
fusible  and  non-conducting  powder  through  which  the  fuse 

is  drawn.  When  it  is 
not  supported  by  the 
fuse  it  is  tied  to  the 
main  arm  in  order  to 
prevent  its  falling  out 
of  position.  The  fuse 
is  maintained  in  its  posi- 
tion between  the  main 
and  auxiliary  arms  by 
the  zinc  jaws  on  the 
top  end  of  the  main  arm 
and  the  zinc  plates  on 
the  auxiliary  arm. 

The  jaws  which  form 
the  terminals  are  car- 
ried by  separate  blocks 
of  marble,  and  are  fur- 
ther insulated  from  the 
marble  of  the  switch- 
board by  means  of  porce- 
lain strips  and  bush- 
Fig.  64.  A  High-Potential  Air-Break  Switch  ingS.  There  IS  also 

mounted   on   the    upper 

marble  blocks  the  latch  which  opens  the  zinc  jaws  on  the 
main  arm.  This  latch  is  operated  to  release  the  fuse  by 
means  of  the  rope  shown  in  the  engraving. 


/  h^m 


GENERATORS,    SWITCHES,   PROTECTIVE   DEVICES      131 

The  operation  of  the  switch  to  rupture  a  loaded  circuit 
is  as  follows  :  With  the  switch  in  its  normal  position,  cur- 
rent is  led  to  the  upper  terminal,  passing  thence  to  the 
zinc  jaws  on  the  main  arm,  from  which  it  passes  through 
the  fuse  to  the  auxiliary  arm,  down  the  auxiliary  arm,  and 
through  the  cable  to  the  lower  blade  on  the  main  arm  ; 
thence  it  passes  out  through  the  bottom  terminal.  A  pull 
on  the  latch  rope  forces  the  jaws  open  and  thereby  releases 
one  end  of  the  fuse,  which  is  then  rapidly  drawn  through 
the  non-conducting  powder  in  the  holder  tube  by  the  fall 


SECTION  OF 
SWITCH  JAW 


ROUND  BRASS 

c 

LU 

Ei 

z 
< 

I 

I 


Fig.  65.    A  "  Ram's  Horn, ' '  Pole-Line  Switch 

of  the  auxiliary  arm  to  its  horizontal  position,  thus  ruptur- 
ing the  circuit  and  blowing  out  the  arc  which  is  formed. 
The  main  arm  is  then  unlocked  from  the  catch,  and  the 
mechanism  of  the  switch  swung  down  to  an  accessible  posi- 
tion, and  the  fuse  replaced.  When  this  is  accomplished,  the 
mechanism  is  returned  to  its  normal  position  by  means  of 


132       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

the  rope  on  the  main  arm.  In  order  to  prevent  the  fuse 
from  rupturing  under  medium  load  and  instantaneous  over- 
loads, it  is  made  heavier  than  it  would  be  were  the  device 
intended  for  automatic  fuse  action  rather  than  a  switch. 

Air-Break  Switches.  —  In  many  long-distance  trans- 
mission plants  in  the  West  the  high-tension  switches 
employed  are  simply  long-break  "stick"  switches  in  which 
the  length  of  the  break  is  depended  on  for  opening  the 
line.  A  common  home-made  switch  of  this  kind  has 
an  inclosed  fuse  attached  to  the  stick  on  which  the 
switch  jaw  is  carried.  When  the  fuse  is  blown  the  switch 
stick  is  pulled  out  and  replaced  by  a  similar  fused  stick, 
as  in  the  case  of  an  ordinary  low-tension  removable  fuse 
holder. 

Another  type  of  home-made  switch  contains  a  short  fuse 
mounted  between  carbon  blocks  under  more  or  less  ten- 
sion. When  the  fuse  is  blown  or  when  a  trigger  device 
which  holds  the  switch  closed  is  tripped,  the  blocks  are 
instantly  thrown  apart. 

These  types  of  combined  stick  switches  and  fuses  are 
generally  made  interchangeable  so  as  to  admit  of  easy 
replacement. 

A  type  of  switch  largely  used  in  Pacific  coast  high- 
tension  practice  is  a  "  ram's  horn,"  air-break,  pole-line 
switch.  Fig.  65  illustrates  a  switch  of  this  kind  which 
has  proven  quite  reliable  in  handling  a  potential  of  33,000 
volts.  The  jaws  of  the  switch  are  placed  side  by  side, 
only  thirteen  inches  apart.  Just  above  the  switch-jaws 
are  two  curved  conducting  strips  made  of  line  wire.  The 
switch  jaws  are  normally  connected  together  by  means  of 
a  cylindrical  brass  rod,  attached  to  a  long  wooden  handle. 
The  jaws  have  a  bayonet  clip  on  their  ends  which  engages 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      133 

the  brass  rod  and  prevents  it  from  falling  out  when  the 
switch  handle  is  released. 

When  the  circuit  is  broken  by  pulling  the  brass  rod  out 
of  the  switch  jaws  by  means  of  the  attached  handle,  the 
arc  which  ensues  is  blown  up  between  the  horns  by  the 
heated  air  currents  until  it  passes  the  point  where  its 
length  is  the  maximum  that  the  voltage  behind  it  will 
maintain,  and  it  breaks. 

Conditions  which  Render  Switching  Necessary.  —  A  care- 
ful consideration  of  the  conditions  under  which  it  becomes 
imperative  to  open  high-tension  transmission  lines  will  lead 
to  the  conclusion  that  such  instances  are  indeed  few. 
The  opening  of  high-voltage  lines  on  the  high-tension  side 
of  transformers  is  one  of  the  most  fruitful  causes  of  trouble 
in  the  operation  of  transmission  lines.  Hence,  for  very 
high  pressures,  switching  either  should  not  be  done  at  all 
or,  if  it  must  be  done,  it  should  be  accomplished  on  the 
low- voltage  side  of  transformers.  There  is,  however,  one 
catastrophe  which  renders  it  unavoidable.  If  a  transformer 
is  in  any  way  set  on  fire,  and  it  becomes  necessary 
to  cut  it  out  without  bringing  about  an  interruption  of 
service,  the  high-tension  switch  must  be  opened  regard- 
less of  line  conditions.  It  is  for  such  infrequent  emer- 
gencies that  a  stanch  and  trustworthy  switch  is  most 
needed. 

The  major  part  of  the  switching  done  under  load  can  be 
equally  well  carried  out  from  the  low-voltage  side  of  trans- 
formers as  from  the  high-tension  side.  The  most  common 
switching  operation  is  that  of  cutting  out  a  bank  of  trans- 
formers. This  operation  can  be  best  done  first  on  the  low- 
voltage  side,  thus  leaving  only  the  transformer  exciting 
current  to  be  cut  off  on  the  high-voltage  side.  In  most 


134      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

cases  it  is  better  to  leave  the  transformers  in  circuit  rather 
than  break  the  high-tension  side  under  no  load.  In  the 
event  of  a  persistent  short  circuit  on  the  high-tension  line, 
it  is  quite  feasible,  and  generally  best,  to  break  the  low- 
voltage  circuits  first. 

Automatic  Station  Protective  Devices.  • —  Perhaps  no 
part  of  the  subject  of  long-distance  transmission  has  re- 
ceived more  attention  than  the  protection  of  high-voltage 
apparatus  from  damage  due  to  abnormal  conditions.  The 
proper  design  and  installation  of  protective  appliances  is  a 
matter  of  far-reaching  importance  in  the  laying  out  of  a 
high-tension  line,  since  the  insertion  of  safety  apparatus 
at  the  proper  point  in  the  line  will  obviate  an  endless 
amount  of  trouble. 

The  several  kinds  of  protective  appliances  used  in  high- 
tension  practice  are  fuses,  circuit  breakers  (either  separate 
or  as  composite  parts  of  oil-break  switches),  overload  re- 
lays, time-limit  relays,  and  reverse-current  relays.  Of  these 
widely  different  devices,  as  regards  the  function  each  is 
designed  to  exercise,  the  fuse  is  the  simplest  means  for 
automatically  breaking  a  circuit. 

Fuses  for  high-tension  alternating-current  circuits  are 
quite  different  from  those  in  use  on  direct-current  lines, 
for  the  reason  that  when  a  fuse  ruptures  on  a  high- 
potential  circuit,  the  arc  that  is  drawn  tends  to  persist, 
owing  to  the  high  voltage  behind  it.  The  current  of  a 
high-potential  line  thus  ruptured  tends  to  maintain  the 
continuity  of  the  circuit  by  following  the  path  of  the 
heated  air;  it  may  also  jump  to  a  point  on  the  other 
side  of  the  line,  and  short  circuit  the  line  between  the 
protective  device  and  the  source  of  supply.  The  one 
object  in  common  in  the  various  kinds  of  fuses  used  in 


GENERATORS,    SWITCHES,   PROTECTIVE    DEVICES     135 

alternating-current  practice  is  thoroughly  to  insulate  the 
fuse  from  the  neighboring  parts  of  the  line.  Thus  it  is 
intended  that  the  suppression  of  the  arc  shall  be  from  the 
fuse  block  into  the  neighboring  air,  thereby  increasing 
the  length  of  the  break,  and  so  effectively  opening  the 
circuit. 

Fuse  blocks  are  generally  mounted  on  the  back  of  the 
switchboard,  either  on  separate  marble  bases  or  near  the 
top,  and  are  rigidly  secured  to  the  board  by  means  of 
brackets  on  the  rear  of  the  board. 

A  type  of  fuse  holder  in  use  on  alternating-current 
circuits  not  exceeding  2,500  volts  in  pressure  is  called  an 
expulsion-block  fuse,  Fig.  66.  It  consists  simply  of  a  porce- 
lain block  in  which  a  rectangular  hole  has  been  cut.  This 
recess  receives  a  block  of  lignum-vitae.  At  each  end  of 
the  porcelain  block  there  is  fitted  a  copper  stud,  which 
extends  through  the  upper  surface  and  is  an  elongation  of 
the  chisel-shaped  contact  piece.  These  also  hold  the 
cover  of  the  block  in  place,  which  is  likewise  made  of 


Fig.  66.     A  Type  of  Lignum-vitae  High-Tension  Fuse  Block 

lignum-vitae  and  fitted  with  an  air- vent,  and  well  insu- 
lated by  thumb-screws  on  the  studs.  The  fuse  is  placed 
under  the  vent  in  the  upper  lignum-vitae  block  and 
between  the  two,  and  is  joined  to  the  copper  studs. 
When  the  fuse  blows  the  arc  takes  place  between  non- 
combustible  material,  and  hence  is  blown  upward  into  the 
atmosphere. 


136       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

When  the  potential  of  the  circuit  exceeds  2,500  volts,  a 
mechanical  device  is  used  to  sever  the  fuse  when  the  tensile 
strength  is  reduced  by  the  heating  produced  by  overload 
currents.  Rupture  of  the  circuit  just  before  the  fusing 
point  is  reached  reduces  the  current  of  hot  air  bridging 
the  gap,  and  consequently  tends  to  suppress  the  ensuing 
arc.  The  tendency  to  emit  showers  of  fused  metal  is  also 
overcome,  and  a  quicker  breaking  of  the  circuit  is  made 
possible.  The  mechanical  means  adopted  to  produce  this 
result  consists  of  a  spring-expulsion  fuse  block  introduced 
in  the  circuit  in  the  same  way  as  the  expulsion  block  already 
described.  It  is  made  up  of  a  base  and  two  side  pieces  of 
hard  wood,  the  whole  being  varnished  and  fireproofed.  On 
the  base  is  fitted  a  lignum-vitae  block,  which  goes  between 
the  terminals  of  the  circuit.  The  fuse  block  is  connected 
to  the  circuit  by  means  of  a  chisel-shaped  piece,  similar  to 
those  used  in  above-described  fuses.  Each  piece  goes 
through  the  base,  and  is  attached  by  means  of  copper  strap 
to  a  copper  plate.  The  copper  plate  has  mounted  on  it  a 
stud  with  a  vent  and  washer,  and  is  in  the  shape  of  an 
inverted  U  ;  the  two  ends  being  carried  on  a  pin  which 
rotates  in  the  plane  of  the  chisel  piece.  A  stout  spring 
mounted  on  the  pin  holds  the  copper  pin  normally  in  a 
recumbent  position  on  the  base  of  the  block.  The  set 
fuse  rests  on  the  lignum-vitae  block,  and  is  long  enough  to 
hold  these  terminals  in  a  vertical  position.  Such  a  fuse  is 
stout  enough  to  overcome  the  tendency  of  the  terminals 
to  spring  back  on  the  base,  but  when  its  tensile  strength 
is  diminished  by  heating,  the  fuse  quickly  blows,  as  above 
described,  and  breaks  the  circuit.  The  current-carrying 
parts  of  the  device  are  completely  inclosed  in  fiber  strips, 
and  a  cover  of  lignum-vitae  with  an  air  vent  is  fitted  over  the 


GENERATORS,   SWITCHES,    PROTECTIVE    DEVICES      137 

top.  To  obviate  the  tendency  to  arc  over  the  sides,  the 
side  pieces  are  extended  several  inches  beyond  the  inclos- 
ing strips. 

When  this  fuse  is  used  for  potentials  greater  than  5,000 
volts,  the  fuse-block  connections  are  thoroughly  insulated 
from  the  switchboard  by  tubes  of  molded  rubber.  These 
also  support  the  block  and  the  connections  to  the  circuit 
behind  the  board  and  several  inches  from  it.  Expulsion- 
type  blocks  are  in  use  to  protect  circuits  operating  under 
tensiyis  as  high  as  20,000  volts  and  carrying  100  amperes. 

Although  the  use  of  fuses  is  quite  extensive  on  circuits 
of  moderate  voltages  and  currents,  it  becomes  impractica- 
ble to  employ  them  on  high-tension  circuits  carrying  large 
power.  Under  these  conditions  it  becomes  imperative  to 
provide  devices  which  will  automatically  open  the  circuit 
mechanically. 

The  overload  relay  is  an  apparatus  which  exercises  a 
function  similar  to  that  of  a  circuit  breaker.  In  its  usual 
form  an  overload  relay  consists  of  a  solenoid  surrounding 
a  soft  iron  rod  or  plunger,  which  is  attracted  upwards  and 
causes  an  auxiliary  bar  to  strike  against  contacts  and  close 
a  local  circuit,  through  the  tripping  magnet  of  an  oil  cir- 
cuit breaker.  In  order  to  adjust  the  position  of  the  plunger 
for  varying  current  strengths  it  is  supported  by  a  disc  in 
a  tube  which  is  fitted  to  the  lower  end  of  the  solenoid.  By 
adjusting  the  position  of  this  disc  vertically  the  plunger 
can  be  set  to  operate  at  any  desired  current  strength. 

In  the  event  that  it  becomes  necessary  to  use  current 
from  a  single  source,  to  actuate  both  the  relay  and  the 
circuit  breaker,  which  means  current  from  the  same  trans- 
former, the  tripping  mechanism  on  the  oil  switch  is  con- 
nected in  series  with  the  relay,  and  the  secondary  of  the 


138       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


current  transformer.  Normally,  this  connection  short  cir- 
cuits the  tripping  mechanism,  and  the  plunger  of  the  sole- 
noid in  this  case  breaks  the  short  circuit  when  it  is  pulled 
upwards,  and  so  permits  the  operation  of  the  tripping 
magnet. 

The  connections  for  both  cases  are  shown  in  Figs.  67 
and  68. 

The  overload    time-limit  relay  is  a  device  intended    to 


STATION    BUS    BARS 


I        I 


SERIES  .  J  ;   : 


CONNECTIONS  O.F  OVERLOAD  RELAY' 
Fig.  67  Fig.  68 

operate  the  circuit  breaker,  should  the  overload  continue 
for  some  definite  length  of  time,  for  which  the  relay  has 
been  set.  Overload  time  relays  are  designed  for  two  kinds 
of  service,  namely,  to  handle  temporary  or  brief  overloads, 
and  to  confine  the  effect  of  an  overload  to  some  local  sec- 
tion of  the  circuit,  and  hence  restore  normal  conditions  by 
causing  the  protective  appliance  in  that  section  to  operate. 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES     139 

The  first  .function  it  must  discharge,  sometimes,  when  lines 
become  crossed  or  short  circuited.  In  such  cases  the  cir- 
cuit often  relieves  itself,  however,  by  burning  out  the 
obstruction,  and  it  would  be  bad  practice  to  open  the 
circuit  unless  the  trouble  is  prolonged. 

When  overload  time  relays  are  used  on  feeders  or  sub- 
feeders    fed  by  an  alternating-current   generator,  a   very 


Fig  69.    Mechanism  of  a  Time-Limit  Relay 


efficient  method  of  protection  is  obtained  by  proper  em- 
ployment of  the  adjustable  time  feature.  By  using  relays 
in  the  main  feeders  designed  to  open  in,  say,  five  or  six 
seconds,  relays  in  the  sub-feeders  which  will  open  in  two 
or  three  seconds,  and  instantaneously  operating  relays  in 


140      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

local  circuits,  an  overload  or  short  circuit  in  the  main 
feeders  would  not  be  relieved  unless  it  continued  for  the 
time  mentioned ;  the  same  trouble  would  not  be  relieved 
in  the  sub-feeder  for  two  or  three  seconds;  while  in  the 
local  circuit  relief  would  occur  instantly.  Time-limit  re- 
lays are  operated  by  clockwork  mechanism.  Fig.  69  shows 
the  mechanism  of  a  time-limit  relay.  Fig.  70,  two  discs  of 
wood,  which  are  carried  by  slowly  rotating  shafts.  Mounted 
on  the  periphery  of  each  disc  is  a  piece  of  copper  strip, 
against  which  is  pressed  a  contact  piece  of  spring  brass. 
A  companion  piece  of  brass  is  so  fastened  as  to  be  just 

•  Copper  Piece 


l| 

A 

1 

B 

Fig  70.    Detail  of  Time-Limit  Relay 

out  of  contact  with  the  top  of  block  A.  On  the  shaft 
which  carries  the  wooden  discs  is  also  mounted  a  notched 
brass  wheel,  which  engages  with  a  detent,  presenting  the 
movement  of  the  clockwork.  On  a  parallel  shaft  which 
revolves  at  a  higher  rate  of  speed  are  four  aluminum  vanes 
at  right  angles  to  each  other  ;  these  are  adjustable  to 
vary  the  time  interval  by  regulating  the  speed  of  the  clock- 
work, which  in  turn  controls  the  speed  of  rotation  of  the 
wooden  discs.  In  most  apparatus  of  this  kind  the  time 
per  revolution  of  the  discs  varies  from  three  to  ten  sec- 
onds. The  contact  points  are  always  connected  in  an  aux- 
iliary circuit,  which  generally  carries  a  direct  current  at  low 
pressure ;  they  are  in  series  with  the  tripping  magnets  of 


GENERATORS,   SWITCHES,    PROTECTIVE   DEVICES      141 

the  oil-break  switch,  and  therefore  control  the  operation  of 
that  switch.  Underneath  a  lever  attached  to  the  ratchet 
above  mentioned  is  a  cylindrical  iron  piece,  about  an  inch 
in  length,  which  is  supported  by  a  spring  that  has  a  vertical 
motion.  Another  similar  iron  piece  and  joined  to  it  is 
mounted  underneath  the  spring  contact  over  the  disc  A. 
A  solenoid  which  is  excited  by  current  transformers  forces 
the  two  iron  pieces  upwards,  whereupon  one  of  them  pulls 
down  the  ratchet.  The  iron  pieces  which  are  thus  attracted 
by  their  cores  are  designed  as  levers.  The  time-limit  relay 
operates  on  the  following  principle :  Assuming  a  short  cir- 
cuit to  have  occurred,  both  of  the  coils  are  magnetized  ;  one 
of  them  releases  the  clockwork,  and  the  other  forces  the  con- 
tact against  the  disc  A.  So  long  as  the  short  circuit  con- 
tinues the  magnets  remain  energized  and  maintain  the 
parts  in  this  condition.  Should  the  short  circuit  continue 
during  the  time  necessary  for  the  discs  to  rotate  far  enough, 
both  contact  pieces  will  impinge  against  the  copper  facings, 
and  so  close  the  auxiliary  line.  If  the  trouble  is  relieved 
before  contact  is  made,  the  iron  pieces  are  drawn  back  into 
their  normal  position  by  retractile  springs,  thereby  pulling 
the  contact  pieces  away  from  the  disc  A,  and  allowing  the 
detent  to  bring  the  mechanism  to  a  stop  after  it  has  made 
one  revolution,  without  tripping  the  circuit  breaker.  Since 
the  solenoids  operate  the  magnetic  plugs  or  cores  against 
the  resistance  of  adjustable  springs,  the  calibration  of  the 
solenoids  is  accomplished  through  the  medium  of  these 
springs. 

In  order  to  protect  all  working  parts  from  injury  the 
mechanism  of  the  time-limit  relay  is  inclosed  in  a  cylin- 
drical glass  case.  It  is  generally  located  on  the  panel  from 
which  all  outgoing  circuits  radiate. 


142      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Reverse-Current  Relays.  —  The  reverse-current  relay 
usually  consists  of  a  direct-current  motor  of  about  one 
sixteenth  or  one  eighth  horse-power,  with  its  field  energized 
by  a  current  transformer  inserted  in  series  with  the  line, 
while  its  armature  is  supplied  with  current  from  a  poten- 
tial transformer  in  parallel  with  the  line.  Mounted  on  the 
motor  frame  are  two  contacts,  to  which  are  connected  the 
terminals  of  the  local  circuit  which  energizes  the  tripping 
mechanism  on  the  oil  switch  in  the  main  circuit,  which  is 
protected  by  the  relay.  The  shaft  of  the  motor  carries  a 
pair  of  U-shaped  carbon  pieces  which  slide  against  these 
contacts.  When  the  current  in  the  line  is  flowing  nor- 
mally, the  motor  tends  to  rotate  away  from  them  ;  but  if 
the  line  current  is  reversed  the  field  current  of  the  motor 
is  also  reversed,  while  the  direction  of  flow  in  the  armature 
remains  the  same.  Hence  the  motor  rotates  in  the 
opposite  direction,  approximately  an  eighth  of  a  revolution. 
This  is  sufficient  to  bring  the  U-shaped  strips  against  the 
contacts,  which  closes  the  magnetizing  circuit  and  trips 
the  circuit  breaker,  or  indicates  the  condition  of  the  circuit 
by  a  visual  signal. 

The  reverse-current  relay  finds  use  on  feeders  between 
central  and  sub-stations  in  high-tension  practice  ;  these 
are  generally  tied  together  by  parallel  lines  protected  by 
automatic  circuit  breakers  at  both  ends.  In  the  central 
station  are  two  sets  of  bus-bars,  from  each  of  which  one 
circuit  leaves,  but  the  lines  are  frequently  connected  to  a 
common  set  of  bus-bars  when  they  reach  the  sub-station. 
Consequently,  heavy  overloads,  or  short  circuits  on  either 
circuit,  will  affect  the  protective  apparatus  on  that  circuit  in 
the  same  way  that  a  short  circuit  on  both  circuits  through 
the  sub-station  bus-bars  would.  It  is  for  this  especial 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES     143 

condition  that  a  reverse-current  relay  is  designed.  The 
incoming  leads  to  the  sub-station  are  protected  by  reverse- 
current  relays,  while  the  outgoing  leads  of  the  generating 
station  are  protected  by  overload  relays.  If  trouble  occurs 
on  either  circuit  such  as  to  cause  the  operation  of  its  pro- 
tecting circuit  breaker  at  the  central  station  end,  power 
will  be  fed  back  to  the  trouble  over  this  line  from  the 
sub-station  ;  this  reverse  flow  of  power  affects  the  opera- 
tion of  the  reverse-current  relay,  thereby  opening  the 
circuit  at  the  sub-station  end  also.  The  other  line  is, 


MAGNET   COIL   ON 
CIRCUIT  BREAKER 


CIRCUIT  CONNECTIONS  OF  REVERSE-CURRENT  RELAY 
Fig.  71 


of  course,  unaffected.  The  reverse-current  relay  also 
finds  especial  application  in  connection  with  rotary  con- 
verters working  in  parallel  with  other  apparatus  for  the 
purpose  of  preventing  the  inverted  operation  of  the 
rotaries  occasioned  by  cutting  off  the  alternating-current 
supply. 

Fig.  71  shows  the  circuit  connections  of  the  reverse- 
current  relay. 

A  reverse-current  time-element  relay  is  a  protective 
appliance  which  combines  the  functions  of  all  three  pieces 
of  apparatus  just  described,  and  operates  to  break  the  cir- 


144      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

cuit  when  a  reverse  current  of  definite  strength  continues 
to  flow  for  a  predetermined  length  of  time.  The  circuit 
breaker  is  actuated  by  differentially  wound  solenoids,  the 
winding  of  one  being  taken  from  a  potential  transformer 
and  that  of  the  other  from  a  series  transformer.  When  the 
circuit  is  working  under  normal  conditions  the  force  exerted 
by  the  solenoid  windings  is  negligible,  each  winding  prac- 
tically neutralizing  the  other.  Should  the  current  attain 
the  value  for  which  the  mechanism  has  been  set,  the  clock- 
work is  released  and  opens  the  circuit,  if  the  trouble  con- 
tinues for  a  definite  period  of  time.  A  reversal  of  the 
current  with  respect  to  its  normal  flow  also  releases  the 
clockwork,  but  regardless  of  the  current  strength  because 
the  influence  of  the  two  solenoids  is  now  cumulative  instead 
of  differential. 

Circuit  Breakers.  —  Circuit  breakers  designed  for  use  on 
high-tension  lines  are  of  materially  different  construction 
from  their  direct-current  progenitors.  In  direct-current 
practice  a  circuit  breaker  is  generally  used  in  conjunction 
with  the  main  switch ;  in  alternating-current  practice  it 
becomes  the  main  switch  itself,  and  may  be  either  operated 
by  hand  or  tripped  automatically  by  electromagnetic  means. 
A  type  of  electro-mechanical  circuit  breaker  in  which  the 
breaking  takes  place  in  oil  is  shown  in  Fig.  72.  It  is  of  the 
three-pole,  double-break  form,  and  is  actuated  by  electro- 
magnets. Like  the  oil  switches  previously  described,  each 
element  of  the  switch  portion  is  contained  in  a  separate 
brick  cell  filled  with  oil.  Each  pole  or  element  has  two 
stationary  contacts,  one  of  which  is  connected  to  the  in- 
coming and  one  to  the  outgoing  leads  of  the  same  phase. 
All  live  parts  are  mounted  on  porcelain  insulators  attached 
to  a  frame  made  of  cast  iron,  which  also  carries  the  oil 


GENERATORS,   SWITCHES,    PROTECTIVE    DEVICES     145 

tanks.  Across  the  top  of  the  masonry  structure  is  placed 
a  soapstone  slab  in  which  strain  insulators  >are  fitted  to 
support  the  cast-iron  frame. 


Fig.  72.     A  Type  of  Oil  Circuit  Breaker  for  High  Voltages 

The  contact  for  each  pole  is  made  up  of  a  U-shaped  piece 
ot  copper  attached  to  the   end  of  a  strong   wooden  rod. 


146      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

When  the  switch  is  closed,  one  of  the  U-shaped  copper 
pieces  electrically  connects  the  two  contacts  of  each  ele- 
ment. A  common  cross-bar  is  attached  to  the  wooden 
bars  at  their  upper  ends.  This  cross-bar  is  manipulated  by 
a  system  of  levers  to  work  in  a  vertical  plane.  The  cross- 
bar is  lifted  -by  the  force  of  the  magnet  which  incloses  it, 
aided  at  the  commencement  of  the  motion  by  a  pair  of  ^bal- 
ancing  springs.  The  breaker  is  fitted  with  a  toggle  joint 
(which  can  be  seen  at  the  left  of  the  illustration)  which 
automatically  locks  the  levers  when  the  breaker  is  closed. 
The  toggle  joint  is  released  by  a  blow  from  a  tripping  mag- 
net, allowing  the  cross-bar  to  drop  by  gravity  and  open  the 
contacts,  its  fall  being  expedited  by  a  pair  of  stout  springs. 
The  first  break  occurs  at  the  main  contact,  and  immediately 
afterward  at  the  removable  plug  fastened  to  the  rigid  con- 
tact ;  and  immediately  afterward  at  the  removable  contact 
set  in  a  hole  on  the  movable  contact.  The  object  of  this 
plug  is  to  dissipate  the  effects  of  the  possible  arcing.  The 
electromagnets  are  energized  by  current  derived  from  any 
convenient  low-pressure  direct-current  source.  It  is  also 
feasible  to  operate  the  circuit  breaker  by  hand. 

The  oil  tanks  are  made  of  thick  sheet  metal,  lined  with 
insulating  cement.  The  level  of  the  oil  in  the  tanks  is 
shown  by  a  small  sight  gauge.  The  controlling  and  indicat- 
ing apparatus  of  the  circuit-breaker  comprise  a  master- 
switch,  a  telltale  indicator  working  on  the  electro-mechan- 
ical principle,  and  an  incandescent  lamp.  Such  apparatus 
is  carried  on  a  convenient  panel.  To  make  the  circuit 
breaker  automatic,  there  is  provided  a  polyphase  overload 
relay,  which  is  energized  from  series  transformers  in  the 
main  circuit.  The  master  switch,  which  is  of  the  drum  type, 
has  marked  on  it  three  positions  —  viz.  "  off,"  "  closed,"  and 


GENERATORS,    SWITCHES,    PROTECTIVE   DEVICES      147 


position  it  will  remain 


0 


Fig.  73.  A  Type  of  Concentric  Cyl- 
inder Arrester 


"open."     If  it  is  put  to  the  "  open 

so  when  the  operator's  hand  is 

removed.      If,  however,  it  is 

thrown  to  the  "  closed"  posi- 
tion, it  will  instantly  turn  to 

the  "  off  "  position,  when  the 

handle  is  released.     When  in 

the  "off"  position,  it  connects 

the    controlling    circuit    in 

such  a  way    that   if    the  oil 

circuit  breaker  is  opened  by  any  of  the  automatic  appli- 
ances the  operator's 
lamp  on  the  stand  will 
be  lighted  and  thus 
call  attention  to  the 
condition  of  the  cir- 
cuit. The  lamp, 
however,  is  not  lighted 
if  the  operator  should 
throw  the  switch 
to  the  "  open "  posi- 
tion. The  electro- 
mechanical telltale 
indicator  consists  of 
an  electromagnet, 
with  its  armature  so 
pivoted  that  it  can  be 
attracted  through  an 
angle  of  90  degrees. 
Each  switch  is  fitted 
with  an  overload  relay 

operating  on  the  principle  of  a  single-phase  induction  motor. 


VERTICAL  SECTION 
OF  LIGHTNING  ARRESTE.R 

Fig.  74 


148       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Types  of  Lightning  Arresters.  —  Fig.  73  shows  an  arrester 
for  high-tension  circuits  made  by  the  Stanley  Electric 
Manufacturing  Company.  Fig.  74  shows  a  vertical  section 
of  the  arrester. 

It  consists  of  two  nests  of  concentric  cylinders  with 
diverging  ends,  which  are  held  in  position  by  perforated 
porcelain  caps  at  the  top  and  bottom,  the  caps  being  rigidly 
attached  to  an  insulated  support  of  either  marble  or  porce- 
lain. The  line  is  grounded  through  the  innermost  cylinder. 
The  porcelain  caps  are  so  grooved  as  to  make  all  spark 
gaps  about  one  sixteenth  of  an  inch  in  width.  The  pur- 
pose of  the  vents  in  the  caps  is  to  provide  a  good  circula- 
tion of  air. 

Between  the  line  terminal  and  ground  connection  there  are 
three  spark  gaps  of  one  sixteenth  inch  width,  thus  making 
a  total  of  three  sixteenths  of  an  inch  air  gap  between 
either  line  wire  and  ground.  With  commercial  frequen- 
cies, it  requires  a  pressure  of  5,000  volts  to  jump  the  gaps  of 
the  arrester,  but  the  very  high  frequency  of  a  lightning  dis- 
charge reduces  the  arcing  potential  to  one  half  this  value. 

The  area  of  the  discharge  gap  is  considerably  increased 
by  the  use  of  concentric  cylinders,  a  large  discharging  area 
being  desirable  to  take  care  of  heavy  discharges.  For 
circuits  of  1,000  volts,  a  double-pole  arrester  connected 
together  by  a  metallic  strip  is  used.  Circuits  of  high  po- 
tential are  protected  by  a  number  of  the  arresters  connected 
in  series,  the  proper  number  for  a  given  high-tension  circuit 
being  arrived  at  by  experiment.  A  choke  coil  is  connected 
between  each  arrester  and  the  apparatus  to  be  protected. 
This  choke  coil  is  made  up  of  parts  so  disposed  relatively 
to  one  another  that  the  coefficient  of  mutual  induction  is 
very  high.  The  coil  comprises  two  parallel  coils  of  insu- 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      149 

lated  copper  strip,  connected  in  series  and  wound  so  that 
the  current  passes  through  them  in  opposite  directions. 
The  proximity  of  the  coils  makes  the  coefficient  of  mutual 
induction  very  high  ;  hence  with  commercial  currents  the 
self-induction  approaches  zero. 

The  operation  of  the  arrester  is  as  follows  :  Lightning 
enters  from  the  line  to  the  middle  cylinder  and  jumps  the 
gaps  in  the  narrow  parts  of  the  arrester;  it  then  passes 


N.D 


GRCfOND 
Fig-  75-    Circuit  Connections  of  Arrester  shown  in  Fig.  73 

from  the  outer  cylinders  to  the  ground  connection.  Should 
the  generator  current  follow  the  discharge,  an  air  current 
is  immediately  set  in  circulation  through  the  vents  of  the 
porcelain  caps  and  between  the  cylinders ;  this  air  current 
blows  the  arc  upwards  into  the  spaces  between  the  horn- 
shaped  ends  of  the  cylinders,  thereby  rupturing  it.  With 
this  type  of  arrester  there  is  used  a  line  discharger,  the 
function  of  which  is  to  remove  static  charges  from  the  line. 


150      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  line  discharger  consists  of  a  very  small  air  gap  in 
series  with  one  or  several  tubes  containing  oxidized  metallic 
particles.  The  tubes  are  about  18  inches  long,  and  have  a 


Fig.  76.    Westinghouse  "Low-Equivalent"  Lightning  Arrester 

resistance  of  about  50  megohms  —  practically  infinite. 
The  small  air  gap  is  put  in  series  with  the  tubes  as  an 
added  precaution  against  grounding  the  line.  A  line  dis- 
charger behaves  as  a  selective  lightning  arrester.  It  pre- 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      151 


6   CHOKE  COILS,   17  TURNS  PER  COIL 


vents  dynamic  currents  from  passing,  but  readily  allows 
static  discharges  of  low  potential  to  pass  through  the  tubes 
and  over  the  minute  air  gaps  and  thence  to  ground. 

The  number  of  tubes  necessary  for  a  circuit  is  governed 
by  the  line  pressure.  Fig.  75  shows  the  way  in  which  a 
high-tension  arrester 
and  line  discharger  are 
connected  in  circuit. 

Fig.  76  shows  a  type 
of  "low  equivalent" 
arrester  made  by  the 
Westinghouse  Company 
and  used  on  one  of  the 
Niagara  Falls  transmis- 
sion lines.  The  circuit, 
after  passing  through  a 
36  inch  fuse  composed 
of  No.  28  German  silver 
wire,  inclosed  in  a  hard 
fiber  tube  of  approxi- 
mately seven  eighths 
inch  diameter,  is  led 
through  an  adjustable 
spark  gap  between  small 
metallic  balls  to  a  bank 
of  ten  arresters,  each  of 
which  has  seven  cylin- 
ders of  non-arcing  metal. 
The  gaps  are  one  thirty-second  of  an  inch  in  length. 
The  diagram  of  the  connections  (Fig.  77)  is  self-explana- 
tory. The  discharge  first  takes  place  over  the  adjustable 
gap  of  three  eighths  inch  between  the  balls  and  then  over 


i     —  .  — 

36  IN.  ENCLOSED  FUSE  NO.  28 

GERMAN   SILVER  WIRE 

ADJUSTABLE 

GAP  3/g 
r  O  O  — 

^^—  -  N 

rOOOOOOO 

^-OOOOOOCh 

LOOOOOOO 

roooooool 

60  GAPS  IN 

0000000 

HDOOOOOCh   SERIES 

ooooooo 

rOOOOOOOJ 

XD  O  O  O  O  O  O 

boooooO] 

^___               LOOOOOOOO 

0 

^^              oooooooi 

z 

£ 

-=^1__^              oooooooo 

J5 

^^                           OOOOOOOO^  GAPS  \N 

BE 

^~~~^.^              oooooooo  SERIES 

I 

^^              oooooooA 

O 

8 

^~~-  —  -^              oooooooo 

^^              oooooooo 

1 

DIAGRAM  OF  ARRESTER 
CONNECTIONS 

Fig.  77- 


152       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

the  60  gaps,  and  through  the  resistance  to  ground.  The 
illustration  (Fig.  76)  shows  the  frame  on  which  the  three 
sets  of  arresters  for  the  three  high-tension  lines  are 
mounted.  The  containing  panels  are  made  of  marble  and 
are  placed  on  three  sides  of  the  frame.  The  frame  is 
placed  on  rollers,  so  that  in  the  event  a  set  of  arresters 
becomes  defective,  the  frame  can  be  trundled  away  and 
another  set  mounted  in  its  place.  Line  connection  is 
made  through  the  fuses  hooking  into  flexible  spring  con- 
tacts at  their  upper  ends.  The  object  of  the  springs  is  to 
permit  of  changing  the  position  of  the  arrester  slightly 
should  this  become  necessary. 

Ground  Detectors.  —  A  reliable  ground  detector  is  an 
essential  part  of  the  protective  apparatus  of  an  alternating- 
current  plant.  As  the  name  indicates,  it  is  a  device  for 
indicating  an  earthed  or  grounded  condition  of  a  line.  In  its 
usual  form  the  device  consists  of  four  fixed  vanes  arranged 
around  a  movable  vane  made  of  aluminum  and  contained 
in  a  suitable  case.  The  movable  vane  is  supported  on  jew- 
eled bearings  and  is  attached  to  a  pointer. 

The  stationary  vanes  are  connected  in  pairs,  each  pair 
by  one  of  the  line  conductors  through  the  medium  of  a 
condenser.  The  fixed  vanes  act  inductively  upon  the  mov- 
able vanes,  and  the  stresses  exerted  by  the  two  pairs  is 
equal  but  opposite  under  normal  conditions.  Hence  the 
movable  vane  assumes  a  position  midway  between  the  fixed 
vanes,  and  remains  thus  whether  the  device  is  charged  or 
not,  and  the  pointer  remains  at  zero,  denoting  freedom 
from  ground. 

When  a  ground  occurs,  the  primary  strip  of  a  condenser 
and  the  movable  vane  become  electrically  connected,  thus 
causing  the  pair  of  fixed  vanes  which  lead  to  that  condenser 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES     153 


Fig.  78.    General  Electric 
Ground  Detector 


to  become  of  like  polarity  with  the  movable  vane,  repelling 
it  and  causing  the  other  fixed  vane  to  be  attracted  by  it. 
The  action  of  the  two  forces  in  the  same  direction  tends  to 
make  the  movable  vane  assume  a  position  completely 
within  the  vanes  charged  oppositely  to  it  ;  hence  the 
pointer  deflects  in  a  direction  which 
indicates  a  ground  on  that  side  of  the 
circuit. 

In  the  best  practice,  the  condensers 
for  charging  the  fixed  vanes  are  inde- 
pendent of  the  instrument,  which  obvi- 
ates all  danger  of  damage  to  the  device 
by  high  potentials  and  also  allows  it  to 
be  installed  wherever  it  is  convenient. 

Fig.  78  shows  a  static  ground  detector  for  high-potential 
circuits. 

Fig.  79  shows  the  connections  of  a  ground  detector  to  a 

three-phase  three-wire  circuit. 
Synchronizing  Devices.  — • 
When  generators  are  operated 
in  parallel  some  device  is  ne- 
cessary to  indicate  whether  or 
not  the  machines  are  in  step 
or  synchronism.  The  ideal 
synchronizing  device  should 
indicate  whether  the  machine 
being  synchronized  is  running 
too  fast  or  too  slow  ;  it  should 
indicate  the  amount  of  differ: 
ence  in  frequency,  and  should  also  indicate  the  condition  of 
synchronism  with  exactness.  The  use  of  lamps  to  indi- 
cate synchronism  is  a  very  unsatisfactory  method  because 


GROUND 

Fig-  79'     Connection  of  Ground  De- 
tector to  Three-Phase  Circuit 


154      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


X 


(L 


tf 


x 


Fig.  80.    Relative  Positions  of 
Coils  of  the  Synchroscope 


they  do  not  perform  the  first  function.  They  discharge 
the  second  function  splendidly  and  the  third  function 
approximately.  In  the  best  modern  central-station  practice 
the  only  synchronizing  devices  employed  are  the  Lincoln 
Synchroscope  and  the  Synchronism  Indicator. 

The  principle  upon  which  the  operation  of  these  two 
synchronizing  devices  depends  is  the  relative  change  in  posi- 
tion assumed  by  a  movable  coil 
suspended  in  the  axis  of  a  station- 
ary coil  when  the  phase-relations  of 
the  currents  in  the  two  coils  differ. 
Thus  for  instance  beginning  with  a 
phase  difference  between  a  mova- 
ble coil  A  and  a  fixed  coil  F  of 
zero,  a  phase  difference  of  90  degrees  will  be  followed  by  a 
corresponding  mechanical  change  in  the  movable  system  of 
90  degrees,  and  each  suc- 
cessive change  of  90  de- 
grees in  phase  will  be  fol- 
lowed by  a  corresponding 
mechanical  change  of  90 
degrees. 

The  movable  system 
comprises  a  second  coil  B 
(Fig.  80)  which  is  securely 
fastened  to  coil  A,  with  its 
phase  90  degrees  from 
that  of  coil  A,  and  the 
axis  of  A  passing  through 

,.  r     r>       -ri  Fig-  81.    The  Synchroscope. 

a  diameter  of  B.    There- 
fore, when  a  current  passes  through  B  the  difference  in 
phase  relation  to  that    in   A  will    always   be  90  degrees. 


GENERATORS,    SWITCHES,   PROTECTIVE    DEVICES       155 

Under  such  conditions  it  is  obvious  that  with  a  difference 
of  phase  between  A  and  F  of  90  degrees,  the  movable  sys- 
tem will  assume  such  a  position  as  will  bring  B  parallel  to 
F  since  the  force  between  A  and  Fis  zero,  and  the  force 
between  B  and  .Fis  a  maximum  :  likewise,  when  the  phase 
between  B  and  F  is  90  degrees,  A  will  be  parallel  to  F. 
For  intermediate  phase  relations  it  can  be  shown  that  under 
certain  conditions  the  position  of  equilibrium  assumed  by 
the  movable  system  will  exactly  represent  the  phase  relations. 
In  the  Lincoln  Synchroscope  (Fig.  81),  the  coil  F  con- 


Fig.  82.    The  Synchronism  Indicator 

sists  of  a  small  laminated  iron  field  provided  with  a  winding 
whose  terminals  are  connected  with  the  lower  binding  posts. 
The  coils  A  and  B  are  windings  practically  90  degrees 
apart  on  a  laminated  iron  armature  pivoted  between  the 
poles  of  the  above  field.  These  two  windings  are  joined 
and  a  tap  from  the  junction  is  brought  out  through  a  slip 
ring  to  one  of  the  upper  binding  posts.  The  two  remain- 
ing ends  are  brought  out  through  two  more  slip  rings,  one 
of  which  is  connected  to  the  remaining  top  binding  post, 


156       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

through  a  non-inductive  resistance,  and  the  other  to  the 
same  binding  post  through  an  inductive  resistance.  A 
light  aluminum  hand  attached  to  the  armature  shaft  marks 
the  position  assumed  by  the  armature,  the  pointer  moving 
around  a  dial  like  the  hands  of  a  clock.  If  the  speed  of 
the  incoming  machine  is  too  fast  the  pointer  rotates  in  the 

CONNECTIONS    WITH    GROUNDED    SECONDARIES    ON 
POTENTIAL   TRANSFORMERS 


ftes/stance-ffeactance  Box 


To  corresponding  phases  of  machines 
or  buses  being  synchronized 


Fig.  83.    Circuit  Connections  of  Synchronism  Indicator 

direction    marked   Fast,  and  if  too  slow,  in  the  opposite 
direction  marked  Slow. 

The  non-inductive  resistance,  which  consists  of  an  incan- 
descent lamp,  and  the  inductive  resistance,  or  choke  coil, 
are  mounted  within  the  case,  thus  making  the  instrument 
self-contained,  no  external  resistance  being  necessary. 


GENERATORS,    SWITCHES,    PROTECTIVE    DEVICES      157 

The  current  taken  by  this  instrument  is  approximately 
one-half  an  ampere  from  each  circuit. 

The  Synchronism  Indicator  (Fig.  82)  is  similar  in  con- 
struction to  a  small  motor ;  the  field  winding  being  ener- 
gized from  the  synchronizing  bus-bars  excited  by  the  machine 
that  is  being  operated.  The  armature  is  drum-wound  and 
consists  of  two  coils  securely  fastened  at  right  angles  to 
each  other  and  connected  in  series. 

Fig.  83  shows  the  connections  of  the  Synchronism  Indi- 
cator in  a  circuit  with  grounded  secondaries  on  potential 
transformers.  A  and  B  are  binding  posts  through  which 
the  field  connections  are  made.  The  binding  post  E  is  the 
connection  of  the  armature  coils  through  a  collector  ring. 

The  other  two  terminals  are  conducted  to  two  additional 
collector  rings,  one  of  which  is  connected  to  the  binding 
post  D,  thence  through  reactance  to  binding  post  F;  the 
other  terminal  is  connected  to  binding  post  C  through  a 
resistance  to  the  same  binding  post  F.  The  synchronizing . 
bus-bars  excited  by  the  machine  to  be  synchronized  are 
then  connected  to  the  binding  posts  E  and  F.  The  resist- 
ance and  reactance  are  placed  behind  the  board,  the  latter 
being  contained  in  a  metal  case,  to  the  outside  of  which  is 
secured  a  socket  containing  an  incandescent  lamp  which 
serves  as  a  resistance.  Synchronism  is  indicated  when  the 
lamps  are  dark. 

BIBLIOGRAPHY 

Alternating  Current  Machines.  —  Sheldon  and  Mason.  D.  Van  Nos- 
trand  Co.,  New  York,  1903. 

Standard  Polyphase  Apparatus  and  Systems.  —  Oudin.  2d  Edition. 
Van  Nostrand  Co.,  New  York,  1903. 

Speed  Regulation  of  Prime  Movers  and  Parallel  Operation  of  Alter- 
nators.—  Steinmetz.  Trans.  Amer.  Inst.  Elect.  Engrs.,  Vol.  18,  p.  741. 


LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


The  Experimental  Basis  for  the  Theory  of  the  Regulation  of  Alter- 
nators. —  Behrend.  Trans.  Amer.  Inst.  Elect.  Engrs.,  Vol.  20,  p.  739. 

A  Contribution  to  the  Theory  of  the  Regulation  of  Alternators.  — 
Hobart  and  Punga.  Trans.  Amer.  Inst.  Elect.  Engrs.,  Vol.  21,  p.  183. 

The  Determination  of  Alternator  Characteristics.  —  Herdt.  Trans. 
Amer.  Inst.  Elect.  Engrs.,  Vol.  19,  p.  1092. 

Compounding  of  Self-Excited  Alternating  Current  Generators  for 
Variation  in  Load  and  Power  Factor.  —  Garfield.  Trans.  Amer.  Inst. 
Elect.  Engrs.,  Vol.  20,  p.  811. 

Parallel  Operation  of  Alternators.  —  Lincoln.  Jour.  Franklin  Inst., 
April,  1902. 

Management  of  Alternators.  —  Hanchett,  Central  Station,  August,  1903. 

Mechanical  Construction  of  Revolving  Field  Generators.  —  Rushmore. 
Trans.  Amer.  Inst.  Elect.  Engrs.,  Vol.  21,  p.  145. 

An  Improved  Method  of  Testing  Large  Alternators  Under  Full  Load 
Conditions.  —  Behrend.  Elect.  World  and  Engineer,  New  York,  Oct.  31, 

I9°3»P-  7i5- 

The  Use  of  Group  Switches  in  Large  Power  Plants.  —  Stillwell. 
Trans.  Amer.  Inst.  Elect.  Engrs.,  Vol.  21,  p.  9. 

Oil-Switches  for  High  Pressures.  —  Hewlett.  Trans.  Amer.  Inst  . 
Elect.  Engrs.,  Vol.  21,  p.  u. 

The  Control  of  High-Potential  Systems.  —  Rice.  Trans.  Amer.  Inst. 
Elect.  Engrs.,  Vol.  18,  p.  407. 

Synchronism  and  Frequency  Indicators.  —  Lincoln.  Trans.  Amer.  Inst  . 
Elect.  Engrs.,  Vol.  18,  p.  255. 

Notes  on  Synchronizing.  —  Roman.  Elect.  World  and  Engineer, 
New  York,  June  14,  1902,  p.  1044. 


CHAPTER    V 

LAWS   GOVERNING   ELECTRICAL   TRANSMISSION 
OF    ENERGY 

Power  in  an  Alternating-Current  Circuit  —  Power  Factor. 

—  In  a  direct-current  circuit  the  power  in  the  circuit  equals 
the  product  of  the  E.M.F.  in  volts  and  current  strength 
in  amperes. 

In  an  alternating-current  circuit  the  instantaneous  power 
equals  the  product  of  the  instantaneous  values  of  current 
strength  and  voltage. 

When  current  and  voltage  are  not  in  phase,  which  is  the 
usual  condition  in  alternating-current  circuits,  there  are 
moments  when  the  pressure  has  a  positive  sign  and  the 
current  a  negative  sign,  and  vice  versa.  The  instantaneous 
power  at  such  moments  is  of  negative  value,  or  power  is  be- 
ing sent  back  into  the  generator  by  the  diminishing  mag- 
netic field  which  had  previously  been  set  up  by  the  cur- 
rent. Hence  the  circuit  is  receiving  power  from  the 
generator  and  returning  it  in  pulsations,  the  frequency  of 
which  is  double  that  of  the  generator  frequency. 

Therefore  the  power  in  an  alternating-current  circuit  is 
not  the  product  of  voltage  and  current  but  depends  on  the 
angle  of  current  lag  (j>.  Denoting  instantaneous  values  by 

('): 
When  the  current  lags  by  the  angle  <f> 

Ef  =  Em  sin  a 
and  for  convenience 

a  =  2  IT  ft 

159 


160       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Then 

/'  =  7m  sin  (a  -  <£) 
and  since 

E  =    -^ 


vr        vi 

the  instantaneous  power 

Pf  =  E' 2'  =  2EI  sm  a  sin  (a  —  <f>). 
But 

sin  (a  —  <£)  =  sin  a  cos  <£  —cos  a  sin  <£, 
thus 

P'  =  2^7  (sin2  a  cos  <j>  —  sin  a  cos  a  sin  </>). 

Since  <£  is  a  constant  the  average  power  through  180°  is 

2^7  cos  <t>  Cn  •  2EI  sin 

7^  =  —  Sinz  a  a  a    — 

TT  Jo  T 

2^*7  COS 


. 
Sin  a  COS  ado. 


["I71"       2,5'7sin  <f>  f  "I77 

J  a  —  I  sm  2  d;  ^  sm"  a 

Jo  TT  J0 


which  gives  P  =  ^"7  cos  «£  =  power  or  energy  in  an  alternat- 
ing-current circuit. 

When  the  current  leads  the  voltage  by  <£°  the  sign  of 
the  power  equation  given  above  becomes  -h,  thus 

P'  =  2  £fsin  a  sin  (a  +  <j>), 
which  equals  the  expression 

P  =  El  cos  <£. 

The  quantity  cos  <£  depends  upon  the  angle  of  lag  or  lead 
of  the  current,  and  is  termed  the  power  factor  of  the  cir- 
cuit. 

The  power  factor  is  the  ratio  of  the  true  watts  to  the 
apparent  watts  or  volt-amperes.  When  the  current  and 
E.M.F.  are  'in  exact  phase,  there  is  no  angle  of  lag,  of 
course,  and  <f>  is  zero  ;  the  power  factor  of  the  circuit  is  then 
unity. 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY  l6l 

Frequency. — The  E.M.F.  wave  of  an  alternator  goes 
through  a  series  of  positive  values  during  the  interval  when 
a  given  coil  on  its  armature  passes  from  a  south  to  a  north 
pole  of  the  field  magnet,  and  through  a  series  of  negative 
values  during  the  interval  when  the  coil  passes  from  a  north 
to  a  south  pole,  or  vice  versa,  according  to  the  coil  connec- 
tions. When  the  E.M.F.  (or  current)  passes  from  zero  to 
maximum  in  one  direction,  falls  back  to  zero,  rises  to  maxi- 
mum in  the  other  direction,  and  returns  to  zero  again,  it 
has  passed  through  a  complete  "  cycle,"  or  two  "alterna- 
tions." A  cycle  is  usually  designated  by  the  tilde  (^). 

The  number  of  cycles  which  an  alternating  current 
passes  through  in  unit  time  —  i.e.,  one  second —  is  termed 
its  frequency,  and  is  usually  denoted  by  the  letter/. 

The  term  "alternations"  is  sometimes  employed,  and 
means  the  number  of  alternations  per  minute,  unless  stated 
to  the  contrary. 

Frequencies  in  use  for  power  transmission  are  generally 
low,  ranging  from  25  to  60  ~  ;  the  lower  value  being  con- 
sidered preferable  when  converters  are  used  on  the  circuit. 
The  higher  the  frequency  of  transmission  the  smaller  be^ 
comes  the  weight  and  cost  of  transformers  and  the  greater 
their  efficiencies. 

Electrical  Factors  of  Power  Transmission.  —  In  the 
transmission  of  electrical  energy  over  long  distances,  the 
following  factors  enter  into  the  design  of  the  system  and, 
in  the  various  ways  peculiar  to  each,  modify  the  character 
of  the  energy  from  that  which  it  possessed  at  the  transmit- 
ting end,  or  interfere  with  the  regulation  of  the  line  :  (i) 
inductance;  (2)  capacity  or  condensance ;  (3)  resist- 
ance ;  (4)  resonance,  which  results  from  a  certain  com- 
bination of  inductance  and  capacity. 


162       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Inductance. — Around  every  conductor  carrying  a  cur- 
rent of  electricity  there  is  set  up  a  magnetic  field  of  force. 
This  field  of  force  is  assumed  to  commence  its  growth 
at  the  axis  of  the  wire  at  the  instant  when  current 
begins  to  flow,  and  in  its  inception  it  is  assumed  every 
line  of  force  composing  it  has  been  cut  once  by  the 
conductor. 

As  the  current  in  the  conductor  grows,  this  ring-shaped 
field  of  force  grows  proportionally.  Conversely,  when  the 
current  decreases,  the  field  of  force  decreases  or  collapses 
correspondingly,  but  the  diameter  of  the  field  may  reach 
zero  value  without  absolute  cessation  of  the  current. 

With  a  definite  strength  of  current  a  conductor  is  en- 
circled by  lines  of  varying  diameter.  If  the  current  is 
decreased,  the  lines  of  smaller  diameter  immediately  col- 
lapse on  the  conductor,  cut  it,  and  disappear  to  a  point  on 
the  axis  of  the  conductor  an  instant  before  it  is  cut  by 
those  of  larger  diameter. 

It  is  obvious  that  the  number  of  lines  of  force,  or,  what 
is  equivalent,  the  strength  of  the  field  of  force,  is  greater 
for  larger  than  for  smaller  currents. 

The  cutting  of  the  conductor  by  these  lines  of  force  sets 
up  an  E.M.F.  in  the  opposite  direction  to  that  of  the  E.M.F. 
causing  the  current  flow  ;  this  is  termed  self-induction,  and 
the  E.M.F.  of  self-induction  is  always  a  counter  E.M.F. 

Self-induction  or  inductance  tends  to  prevent  the  start- 
ing, stopping,  or  change  in  strength  of  an  electric  current. 
On  starting  up  a  current,  the  pressure  of  self-induction 
retards  its  flow  and  so  prevents  it  from  attaining  an  in- 
stantaneous maximum  value.  On  stopping  a  current,  the 
E.M.F.  of  self-induction  retards  its  diminution  and  tends  to 
keep  up  the  flow  in  its  original  direction, 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY          163 

The  coefficient  of  self-induction  is  that  number  by  which 
the  time  rate  of  change  of  current  in  a  circuit  must  be 
multiplied  in  order  to  give  the  E.M.F.  induced  in  that  cir- 
cuit. Its  numerical  value  equals  the  number  of  magnetic 
lines  of  force  linked  with  a  circuit  per  absolute  unit  of  cur- 
rent flowing  in  the  circuit.  The  definition  of  "leakage" 
is  the  total  number  of  lines  inclosing  each  portion  of  the 
circuit. 

The  absolute  unit  of  self-induction  being  too  small  for 
most  determinations,  a  practical  unit  called  the  henry 
is  used,  the  value  of  which  is  io9  times  the  absolute 
unit. 

A  circuit  has  an  inductance  of  one  henry  induced  in  it 
when  a  uniform  rate  of  change  of  current  of  one  ampere 
per  second  produces  a  counter  E.M.F.  of  one  volt. 

The  physical  effect  of  inductance  in  an  alternating-cur- 
rent circuit  is  not  only  to  oppdse  the  current  flow,  but  also 
to  make  the  current  lag  behind  the  E.M.F.,  producing 
it,  in  the  successive  rising  and  falling  between  zero  and 
maximum. 

The  inductance  of  a  circuit  may  be  made  up  of  two 
components :  self  and  mutual  inductance.  The  former 
occurs  when  the  circuit  is  entirely  isolated,  the  latter 
when  the  circuit  is  influenced  magnetically  by  an  adjacent 
circuit. 

Mutual  inductance  is  due  to  lines  of  force  which  sur- 
round one  conductor  cutting  a  second  conductor  in  the 
neighborhood  of  it  and  thus  setting  up  an  E.M.F.  in 
the  second  conductor.  Such  an  E.M.F.  may  either 
oppose  or  assist  the  current  already  flowing,  accord- 
ing to  the  relative  directions  of  the  currents  in  the  two 
circuits. 


164       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Inductance    is  represented   by   the  letter   L.     Mutual 
inductance  is  represented  by  the  letter  M. 

Inductance  may  be  expressed  in  three  ways,  thus, 

_ 

~ 


/108 

where  4>t  is  the  instantaneous  value  of  the  flux  through  a 
coil  of  wire,  /  the  number  of  turns  of  wire  in  the  coil, 
and  /  the  instantaneous  value  of  the  current  in  amperes  ; 
again, 


where  e  =  instantaneous  value  of  the  induced  E.M.F.  in 


volts  and/ — /the   time   rate   of  change   of  current;  and 
I  a* 

once  more, 


where  J  is  the  energy,  in  joules  or  watt-seconds. 

Mutual  Inductance  of  Circuits.  —  The  conductors  of  an 
overhead  circuit  strung  on  the  same  pole  line  exercise  a 
mutually  inductive  action  upon  each  other,  an  alternating 
current  in  one  tending  to  induce  an  alternating  E.M.F. 
in  the  other,  and  the  direction  of  the  induced  E.M.F. 
being  opposite  to  that  of  the  inducing  current.  Hence  if 
two  alternating  currents  flowing  in  parallel  conductors 
have  the  same  phase  relation  they  tend  to  oppose  each 
other;  but  if  they  differ  in  phase  by  1 80°,  which  means 
that  they  flow  in  exactly  opposite  directions  at  any 
given  instant,  their  action  will  be  a  mutually  aiding 
one. 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY          165 

Assuming  the  angles  of  lag  of  the  currents  in  two  or 
more  parallel  conductors  coming  from  the  same  leads  of  an 
alternating-current  source  of  supply  to  be  approximately 
equal,  their  phase  relations  will  be  the  same,  and  they  will 
exercise  an  opposing  action  upon  each  other.  Such  oppo- 
sition tends  to  increase  the  voltage  drop  in  a  manner  sim- 
ilar to  self-induction. 

Under  practical  conditions  two  alternating  currents 
coming  from  separate  generators  do  not  continue  exactly 
in  phase  except  for  short  intervals  of  time,  hence  their 
mutually  inductive  action  produces  an  opposing  effect 
upon  the  currents  at  one4nstant,  and  an  aiding  effect  at 
another  instant,  the  character  of  the  inductive  effect 
changing  with  each  change  of  phase  relation. 

Inductive  Reactance.  —  Reactance  is  the  effect  of  either 
self-induction  or  capacity,  and  is  expressed/!^  ohms.  In- 
ductive reactance  is  numerically  equal  to  2  irfLt  /repre- 
senting the  frequency  of  the  alternating  current  in  cycles 
per  second.  The  symbol  is  Xt.  The  effect  of  inductive 
reactance  in  a  transmission  circuit,  or  in  the  apparatus  con- 
nected therein,  is  to  increase  the  angle  of  lag  and  also  the 
wattless  component  of  the  current.  This  component  of 
the  current  is  in  quadrature  with  the  energy  current  and 
does  no  useful  work  in  a  circuit. 

The  effect  of  the  wattless  component  is  to  increase  the 
total  current,  and  thus  increase  the  heating  of  the  con- 
ductors. 

In  aerial  wires  of  small  resistance  reactance  becomes 
relatively  very  prominent.  Hence  it  is  important  in  some 
cases  that  conductors  of  moderate  cross-section  be  adopted 
for  transmission  purposes. 

Since  inductance  is  proportional  to  the  number  of  mag- 


166       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

netic  lines  linked  with  a  circuit,  the  farther  apart  the  cir- 
cuit conductors  the  greater  will  be  the  inductance,  because 
the  number  of  magnetic  lines  is  greater.  When  the  inter- 
axial  distance  between  wires  is  very  slight,  the  lines  of 
force  which  encircle  each  wire  are  neutralized  by  those  of 
the  other  wire ;  therefore  the  effect  of  inductance  can  be 
reduced  by  placing  the  wires  close  together. 

With  high-tension  overhead  wires,  however,  this  remedy 
is  entirely  impracticable,  owing  to  the  possibility  of  short 
circuits  between  the  conductors,  and  also  the  losses 
which  would  ensue  from  leakage  and  electrostatic  induc- 
tion between  the  wires.  In  high-tension  practice  the 
three  general  methods  used  to  reduce  line  inductance 
are  :  subdividing  the  conductors  or  using  stranded  con- 
ductors of  the  same  total  cross-section  as  the  solid  con- 
ductor which  would  be  required  :  or  balancing  the  effect 
of  inductance  with  artificial  capacity  (condensers  or  con- 
densive  apparatus  introduced  in  the  circuit  at  definite 
intervals). 

The  simplest  means  of  decreasing  mutual  inductance  is 
to  increase  the  inter-axial  distance  between  the  conductors. 
The  practical  limitation  of  this  method  is  the  necessity  of 
carrying  the  circuits  on  the  same  pole,  so  that  mutual  in- 
ductance can  only  be  reduced  in  practice  either  by  placing 
the  conductors  equidistant  from  each  other,  so  that  any 
one  wire  will  be  affected  equally  by  the  wires  of  the  other 
circuit,  or  else  by  transposition  of  the  conductors  with 
respect  to  each  other  at  symmetrical  intervals  along  the 
line. 

Fig.  84  shows  the  latter  method  diagrammatically 
as  applied  to  a  three-phase  circuit.  In  this  method,  which 
is  also  used  in  high-tension  practice,  an  equal  length 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY        l6/ 

or  distance  of  one  conductor  neutralizes  the  action  of 
an  equal  length  of  conductor  of  another  circuit.  Thus 
the  inductive  action  of  one  circuit  upon  the  other  is 
nugatory. 

Capacity  or  Condensance.  —  The  capacity  of  a  con- 
ductor is  the  property  which  it  possesses  of  being  able  to 
receive  a  "charge"  of  electricity.  The  capacity  of  a 
conductor  through  which  an  alternating  current  is  flowing 
is  analogous  to  the  electrostatic  capacity  of  a  Leyden  jar 
or  a  condenser ;  the  unit  of  capacity  is  the  farad,  but 
actual  capacity  values  are  so  small  that  they  are  commonly 
expressed  in  microfarads.  A  condenser  would  possess  a 


Fig.  84.     Method  of  Transposing  a  Three-Phase  Circuit 

capacity  of  one  farad  if  it  were  capable  of  taking  a  charge 
of  one  coulomb  at  a  potential  of  one  volt ;  or  the  numeri- 
cal value  of  the  capacity  of  a  condenser  in  farad  measure 
is  equal  to  the  quantity  of  electricity  which  must  be  de- 
livered to  it  in  order  to  increase  the  difference  of  potential 
between  its  terminals  from  zero  to  one  volt. 

The  farad  is  io~9  times  the  absolute  unit.  The  micro- 
farad is  y-Q^iro  Q~O  °^  a  farad>  or  IO~~15  times  the  absolute 
unit  of  electrostatic  capacity. 

The  charging  or  discharging  current  of  a  condenser 
attains  its  maximum  value  when  the  rate  of  variation  of 
effective  pressure  is  maximum,  or  when  the  E.M.F.  is  of 
zero  value  at  the  instant  of  passing  from  negative  to 
positive  value,  or  vice  versa.  Hence  the  physical  effect 


168       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

of  capacity  is  exactly  opposite  to  that  of  inductance  and 
may  entirely  neutralize  it. 

Under  certain  conditions  the  effect  of  capacity  may 
cause  the  current  to  lead  the  E.M.F.  in  phase. 

In  long-distance  transmission  lines  the  capacity  of  the 
circuits  is  often  of  very  great  magnitude,  and  may  require 
a  large  reserve  in  the  kilowatt  capacity  of  the  gen- 
erators to  charge  the  line  before  working  current  can  be 
gotten  through. 

Capacity  in  an  alternating-current  circuit  produces  an 
effect  measured  in  ohms  and  termed  "  capacity  reactance." 
Thus  in  a  circuit  having  capacity,  the  flow  of  current  in- 
creases in  direct  proportion  with  it  and  the  frequency ; 
hence  the  reactance  due  to  capacity  is  inversely  propor- 
tional to  these  quantities.  Capacity  reactance  has  the  nu- 
merical value  expressed  by  the  equation 


"C  f/~i     ' 

2  TT/C 

C  representing  the  capacity  in  parts  of  a  farad.  The  ef- 
fect of  capacity  in  transmission  lines  can  be  overcome  in 
two  different  ways  :  (i)  by  increasing  the  distance  between 
the  conductors  and  their  distance  from  the  earth ;  the  de- 
crease in  capacity  by  doubling  the  distance  between  con- 
ductors may  amount  to  as  much  as  15  per  cent;  (2)  by 
the  use  of  inductive  apparatus  in  circuit.  Artificial  regu- 
lating impedance  coils  may  be  used  to  accomplish  this 
result. 

The  effect  of  line  capacity-current  varies  only  with  the 
voltage  and  frequency.  As  the  load  decreases  its  influence 
decreases,  for  when  the  load  is  light,  it  is  not  only  entirely 
neutralized  by  inductance,  but  also  becomes  negligible  on 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY  169 

account  of  the  presence  of  a  considerable  current  in  phase 
with  the  E.M.F. 

At  periods  when  both  capacity  and  inductive  loads  of  a 
line  are  reduced,  the  line  capacity-current  causes  the  most 
disturbance  to  regulation,  and  on  such  occasions  attempts 
to  neutralize  the  capacity  effect  with  inductive  apparatus 
which  is  thrown  off  at  the  same  time  acts  only  to  augment 
the  disturbance. 

Resistance.  —  An  alternating-current  circuit  possesses 
resistance  just  as  does  a  direct -current  circuit.  The  resist- 
ance of  an  alternating-current  circuit,  though  usually  insig- 
nificant in  comparison  with  the  other  characteristics,  is  not 
always  negligible. 

If  the  cross-section  of  a  conductor  through  which  an  al- 
ternating current  is  flowing  be  divided  into  numerous  par- 
allel components  or  filaments,  it  is  apparent  that  those 
components  nearer  the  center  suffer  greater  inductive 
effects  than  the  components  nearer  the  interior.  Hence 
the  streams  of  current  near  the  surface  meet  with  less 
opposition  and  attain  their  maximum  value  sooner  than 
those  in  the  central  portions  of  the  conductor.  In  case 
the  conductor  is  of  large  area  and  is  carrying  large 
currents  of  high  frequency,  a  condition  may  be  attained 
in  which  the  central  section  of  a  conductor  may  not  only 
have  no  current  flowing  through  it,  but  under  certain 
circumstances  the  flow  of  current  may  be  in  the  opposite 
direction. 

The  reduction  of  the  effective  cross-section  of  a  conduc- 
tor due  to  this  phenomenon  causes  an  increase  of  effective 
resistance,  so  that  a  current  of  slightly  smaller  value  will 
flow  than  would  be  the  case  if  only  the  true  resistance 
and  inductance  of  the  conductor  be  considered. 


LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

This  apparent  increase  in  resistance  is  termed  the  "  skin- 
effect."  For  all  practical  purposes  it  is  the  same  as  true 
resistance,  and  is  expressed  in  ohms.  In  most  practical 
cases  it  is  negligible. 

Impedance.  —  The  resistance  and  reactance  of  an  alter- 
nating-current circuit  combined  constitute  its  impedance. 
Impedance  is  the  total  opposition  to  the  flow  of  current  in 
a  conductor  and  is  expressed  in  ohms,  so  that  with  a  defi- 
nite impressed  E.M.F.  the  impedance  fixes  the  maximum 
current  that  can  flow. 

The  numerical  value  of  impedance  is  expressed  by  the 
equation, 


z  = 


Resultant  Impedance  of  Several  Impedances  in  Series.  — 
When  a  circuit  includes  two  or  more  pieces  of  apparatus 
in  series,  each  of  which  may  or  may  not  have  resistance,  in- 
ductance, and  capacity,  the  current  which  flows  under  any 
impressed  E.M.F.  has  the  same  phase  throughout.  The 
E.M.F.'s  at  the  terminals  of  the  different  pieces  of  appa- 
ratus may  be  of  different  phases,  depending  upon  the  in- 
ductance and  capacity  of  each,  and  the  magnitude  of  each 
E.M.F.  will  depend  on  the  impedance  of  the  device. 
The  determination  of  the  E.M.F.  necessary  to  force  a 
definite  current  through  a  series  circuit  of  the  kind  men- 
tioned is  analytically  expressed  by  the  equation, 


and  since  E  =  f  Z,  the  total  impedance   of  the    several 
impedances  in  series  is, 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY          I/I 

from  which  it  is  obvious  that  the  total  impedance  is  not 
the  arithmetical  sum  of  the  individual  impedances. 

When  a  circuit  has  impedances  in  series  and  in  parallel, 
or  a  series-parallel  combination,  the'  equivalent  impedance 
is  determined  by  calculating  the  joint  impedances  of  each 
parallel  group  and  combining  them  in  series. 

Admittance,  Susceptance,  and  Conductance.  —  The  ad- 
mittance of  a  circuit  is  the  reciprocal  of  the  impedance,  in 
formula  shape, 


The   equivalent   admittance    of    several    admittances    in 
parallel  is  equal  to 


V(S  Inductances)2  +  (2  Susceptances)2 

The  susceptance  of  a  circuit  is  the  quantity  by  which 
E  must  be  multiplied  in  order  to  give  the  component  of  / 
perpendicular  to  E. 

Its  numerical  value  equals 


in  which  $  is  the  "angle  of  lag,"   sin   </>  is  the  "induc- 
tance factor  "  of  the  circuit. 

The  susceptance  may  also  be  numerically  expressed  by 


b  = 


X2  ' 


X  being  the  equivalent  reactance,   or  the  difference  be- 
tween the  inductive  and  capacity  reactances. 

The  conductance  of  a  circuit  is  a  quantity  by  which  E 


1/2       LONG-DISTANCE  ELECTRIC   POWER  TRANSMISSION 

must  be  multiplied  in  order  to  give  the  power  component 
of  the  current,  or  the  component  in  phase  with  the  im- 
pressed E.M.F.  The  symbol  is  G,  and  the  numerical  value 
is  given  by  the  equations 


and  „ 

Lr  = 


+  X2 


From  the  latter  expression  it  is  evident  that  conduc- 
tance is  not  the  reciprocal  of  resistance,  although  the  two 
properties  are  opposite  in  character. 

Resonance.  —  Resonance  in  an  alternating-current  cir- 
cuit is  that  condition  which  enables  a  definite  E.M.F.  to 
produce  maximum  current  flow  at  a  critical  frequency. 
Resonance  takes  place  when  the  total  inductive  reactance 
equals  the  total  capacity  reactance  ;  or,  stated  differently, 
when 


then  the  two  reactances  entirely  neutralize  each  other; 
the  electrostatic  energy  in  the  condensive  part  being  given 
back  to  the  line  when  the  electromagnetic  energy  of  induc- 
tance is  being  stored  in  the  line.  When  this  occurs  the 
circuit  is  said  to  be  "  tuned  "  for  the  definite  periodicity 
shown  by  the  equation 

i  —     "          •/  * 


2   7T 


Hence  at  that  particular  periodicity  the  impedance 
equals  the  resistance,  and  a  given  E.M.F.  will  send  through 
the  circuit  the  maximum  current  possible. 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY    173 

Injury  to  the  circuit  from  electrical  resonance  may  occur 
when  the  inductance  and  capacity  are  in  parallel,  or  are 
balanced,  thus  causing  currents  of  enormous  values  to  flow 
between  the  two,  because  each  is  always  prepared  to  receive 
the  energy  discharged  by  the  other,  with  the  result  that  a 
see-sawing  or  surging  action  is  set  up  between  the  two, 
and  this  constantly  increases,  due  to  the  receipt  of  energy 
from  the  line.  This  surging  or  resonance  effect  is  liable 
to  overload  the  conductors  between  the  capacity  and  induc- 
tance, and  may  sometimes  destroy  them  by  the  heating 
produced. 

If  the  inductance  and  capacity  be  in  series,  the  effect  of 
resonance  may  raise  the  potential  to  such  a  value  as  to 
break  down  the  insulation  of  the  generator  or  of  apparatus 
along  the  line. 

In  most  long-distance  lines  the  inductances  and  capaci- 
ties are  connected  in  parallel,  and  a  resonant  or  distortion- 
less condition  seldom  occurs. 

Mr.  Paul  M.  Lincoln  has  expressed  the  opinion  (Trans. 
A.  I.  E.  E.,  Vol.  20)  that  "  Considerations  of  voltage  regu- 
lation at  the  receiving  end  of  a  line  limits  the  voltage  drop 
due  to  resistance  in  that  line  to  about  15  per  cent  as  a 
maximum,  and  the  same  consideration  should  keep  the 
inductance  volts  within  a  maximum  of  20  per  cent.  With 
a  power  factor  of  85  per  cent  this  means  a  line  regulation 
of  24  per  cent."  He  also  states  that  "since  the  charging 
current  depends  directly  upon  the  frequency  and  the  press- 
ure, the  apparent  energy  at  60  cycles,  which  is  represented 
in  charging  a  two-hundred-mile  three-phase  line,  is  almost 
equal  to  the  maximum  capacity  of  that  line  limited  by  the 
20  per  cent  inductance  volts  consideration.  At  25  cycles 
the  effect  of  charging  current  is  not  appreciable." 


LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 


ELECTRICAL  CONSTANTS  OF  CERTAIN  TRANSMISSION  LINES. 

STANDARD  ELECTRIC  Co.  OF  CALIFORNIA. 

Data  :  Length  of  line  approximately    ......................  150  miles 

Aluminum  conductors  of    ....................  75  in  diameter 

Area  of  conductors  ............................  471,034  C.M. 

Maximum  resistance  per  mile  at  70°    ................  "  >2O5  ohms 

Frequency  .........................................  6o^w 

Voltage  of  transmission  .............................  60,000 

Distance  between  centres  of  conductors  ...................  42' 

Inductance  of  150  mile  line,  or  300  mile  transmission  .........  0.48  henry 

Inductive  reactance  per  mile  of  conductor,  or  \  mile  of  transmission  at 

6o^/  .........................................  ...  .634  ohms 

(If   30-^  were   used  the   inductive   reactance    would    be    nearly  halved, 

or  ...........................................  °-3775  ohms) 

Impedance  factor  of  line  (impedance  -r-  resistance)  at  6o^«w  .....  3.25  ohms 

(If  30^  were  used  the  impedance  factor  would  be  ...........  1.84  ohms) 

Resistance  of  300  miles  of  conductor  (2  wires  of  150  mile  transmission) 

.................................................  61  .5  ohms 

Inductive   reactance  of  300   miles  of  line   at   6o-»»  (2   wires  of  150  mile 

transmission)  ......................................  190.2  ohms 

(If   30^   were    used  the    inductance    reactance   of    the   line   would    be 

...............  ..................................  95.  i  ohms) 

Impedance  of  300  miles  of  wire  at  6o-«-'  .....................  200  ohms 

(If  30^  were  used  the  impedance  would  be  ................  1  13.2  ohms) 

Capacity  of  the  1  50  mile  transmission  or  300  miles  wire  (considered  as  two 

parallel  cylinders)  ....................................  i  .43  m.f  . 

Capacity  per  mile  of  transmission  line   .....................  0.0095  m.f. 

Capacity   reactance  between   2    wires,  per  mile   of  transmission  at  60^ 

...............................................  279,000  ohms 

(If  30^  were  used,  the  capacity  reactance  between  2  wires  per  mile  of 

transmission  would  be    ...........................  558,000  ohms) 

Capacity  reactance  between   two  wires  of  1  50  mile  transmission  at  60  ^ 

................................................  1,855    ohms 

(If  3O>-w  were  used  the  capacity  reactance  between  two  wires  of  150  mile 

transmission  would  be  ...............................  3»72°  ohms) 

Capacity  or  charging  current  between  two  wires  of  1  50  mile  transmission 

at  6o^<  and  60,000  volts  .........................  32-25  amperes 

If  30^  were  used,  the  charging  current  (at  the  same  voltage)  between  two 

wires  of  150  mile  transmission  would  be  .............  16,125  amPeres 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY          175 

Apparent  power  required  to  charge  the  line   at  6o~w   and   60,000  volts 

3>348  kilowatts 

Real  energy  to  charge  line  at  6o^w  and  60,000  volts    32  kilowatts 

Apparent  energy   to   charge   line   if    30^—'    cycles   and  60,000    volts  were 

used 1,674  kilowatts 

Real  energy  to  charge  line  at  3**^  and  60,000  volts 16  kilowatts 

10,000  kw.   at  60,000  volts  and  unity  power  factor  requires  96.3  amperes 

per  wire. 

The  loss  in  150  mile  transmission  is 855.5  kilowatts 

Per  cent  loss  in  transmission    8.55 

Volts  loss,  per  pair  of  wires  in  150  mile  transmission  at  60^*  .  .  19,260  volts 
Per   cent    volts   loss,  per  pair  of  wires  in   150  mile  transmission  at  6o-»^ 

32.1  per  cent 

Volts  loss,  per  pair  of  wires,  in  150  mile  transmission  at  30^  .  .  10,901  volts 
Per  cent  volts  loss,  per  pair  of  wires,  in  150  mile  transmission  at  30^ 

18.2 

The  capacity  effect  on  a  150  mile  transmission  line  was 
demonstrated  by  considering  a  single-phase  transmission  of 
3,000  kilowatts  at  the  distributing  end,  the  pressure  50,000 
volts  being  kept  constant  at  the  sub-station. 

The  fairly  correct  supposition  was  used  by  considering 
the  line  as  shunted  at  the  generator  and  at  the  sub-station 
by  two  condensers  each  of  one  sixth  the  capacity  of  the 
line,  and  in  the  middle  by  a  condenser  of  two  thirds  the 
line  capacity. 

With  the  line  open  at  the  sub-station,  the  generator 
pressure  is  only  47,676  volts,  the  line  capacity  causing  the 
rise  at  the  sub-station  to  50,000  volts. 

With  3,000  kilowatts  at  unity  power  factor  at  the  receiv- 
ing end,  the  current  required  is  60  amperes  at  50,000  volts. 
The  32.25  amperes  charging  current  when  combined  at 
right  angles  with  the  60  amperes  power  current,  requires 
69.2  amperes  at  the  generator,  the  resulting  generator 
pressure  being  58,800  volts.  With  3,000  kilowatts  at  a 
power  factor  of  80  per  cent  at  the  receiving  end,  the  cur- 


1/6       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

rent  required  is  75  amperes  at  50,000  volts,  or  60  amperes 
power  current  and  45  amperes  inductive  current.  The 
32.25  amperes  of  charging  current,  when  combined  with 
the  60  amperes  power  current  and  45  amperes  inductive 
current,  requires  but  62.1  amperes  at  the  generator,  the 
resulting  generator  pressure  being  60,000  volts.1 

The  following  quantities  are  a  few  of  the  constants  of 
the  Bay  Counties  Power  Company's  line  • 

Capacity  of  150  mile  circuit  =   3  microfarads.     Under 
a  working  potential  of  40,000  volts  there  are  : 
i  X  (3  X  io-6)  (40,000  X   V2)2    =  4,800    watt-seconds   = 
4,800  joules,  or  3, 500  foot-pounds  of  energy  in  electrostatic 
capacity  stored  in  the  circuit  when  it  is  fully  charged. 

Charging  current  at  40,000  volts  and  6o~~  =  45  am- 
peres. 

The  rate  of  supply  of  energy  to  the  circuit  by  the  gen- 
erators and  absorption  from  the  circuit  by  the  generators  is 

45   X  40,000  X  2  .   —   =   1,150,000     watts  =  1,150,000 

joules  per  second  =843,000  foot-pounds  per  second. 

The  generator  gives  out  current  continuously  to  the  line 
for  one  fourth  cycle.  Hence  the  received  or  delivered 
energy  during  a  half  alternation  is  equivalent  to  the  energy 
stored  in  line  capacity,  3,500  foot-pounds  as.  above. 

To  charge  the  line  as  a  condenser  requires  the  capacity 
of  a  2,000  kilowatt  generator. 

1  The  above  data  are  taken  from  Professor  C.  L.  Cory's  paper  on  Trans- 
mission System  Regulation,  read  before  the  Pacific  Coast  Transmission 
Association,  June,  1900. 


LAWS  GOVERNING  TRANSMISSION  OF  ENERGY  177 

BIBLIOGRAPHY 

The  Theory  and  Calculation  of  Alternating  Current  Phenomena.  — 

Steinmetz.     McGraw  Publishing  Company.     N*ew  York.     1902. 

Alternating    Currents.  —  Franklin    &    Williamson.      Second    Edition. 
Macmillan  Co.     New  York.      1901. 

Alternating-Current  Machines.  —  Sheldon  &  Mason.     Third   Edition. 
D.  Van  Nostrand  Co.     New  York.      1903. 

Choice  of  Frequency  for  Very  Long  Lines.  —  Lincoln.    Transactions 
American  Institute  Electrical  Engineers,  Vol.  20,  p.  1231. 

Alternating   Currents. —  Hay,      D.  Van   Nostrand   Company.      New 
York.     1906. 


CHAPTER  VI 
THE   TRANSMISSION  LINE 

Kinds  of  Conductors.  —  In  electrical  transmission  plants 
the  line  represents  a  greater  financial  expenditure  than  any 
other  part  of  the  electric  property.  Upon  its  proper  de- 
sign and  installation  depend  not  only  the  economical  and 
efficient  transmission  of  the  developed  power,  but  also  the 
satisfactory  operation  and  regulation  of  all  the  apparatus  in 
circuit ;  which  also  means  the  satisfactory  working  of  the 
line  under  different  conditions  of  load. 

While  refinements  of  design  and  construction  are  largely 
governed  by  the  conditions  to  be  met  in  each  particular 
case,  it  is  never  advisable  in  the  development  of  electric 
transmission  properties  to  perfect  the  generating  equipment 
at  the  expense  of  the  transmission  equipment.  The  bad 
regulation  and  the  energy  losses  which  ensue  from  faulty 
line  construction  greatly  overbalance  the  efficiency  which 
is  gained  by  undue  attention  to  the  generating  end  of  the 
problem 

The  design  and  construction  of  transmission  lines  are 
governed  by  several  factors  :  ( i )  the  amount  of  energy  to 
be  transmitted  ;  (2)  the  working  potential  to  be  employed; 
(3)  the  length  of  the  line;  (4)  the  climatic  conditions  of 
the  country  which  it  traverses ;  and  (5)  the  permissible 
losses  in  line  drop  and  leakage. 

The  choice  of  conductors  is  confined  to  two  metals, 
namely,  copper  and  aluminum.  Copper,  by  reason  of  its 
high  conductivity,  mechanical  strength,  ductility,  and  free- 

178 


THE   TRANSMISSION    LINE  1/9 

dom  from  corrosion  is  more  extensively  employed  in  high- 
tension  practice  at  the  present  time  than  aluminum.  It  is, 
however,  being  largely  displaced  by  aluminum,  on  account 
of  the  superior  advantages  which  the  latter  metal  offers  in 
lightness,  and  the  consequent  reduction  in  the  weight  to 
be  carried  by  insulators,  pins,  and  cross-arms. 

In  tensile  strength,  hard-drawn  copper  ranges  from 
60,000  to  70,000  pounds  per  square  inch,  while  soft-drawn 
copper  has  a  tensile  strength  of  from  25,000  to  35,000 
pounds  per  square  inch.  The  specific  resistance  of  hard- 
drawn  copper,  on  the  other  hand,  is  from  2  to  4  per  cent 
greater  than  that  of  the  soft-drawn  metal.  Hard-drawn 
copper  is  also  very  brittle  and  inflexible  and  hence  in  large 
sizes  is  very  difficult  to  handle. 

The  tensile  strength  of  aluminum  ranges  from  20,000  to 
3  3,000  pounds  per  square  inch,  and  its  specific  conductivity 
is  only  63%  of  that  of  copper  of  the  same  purity  (com- 
mercial quality).  Hence  in  wires  of  equal  sizes  and 
lengths  aluminum  must  have  a  sectional  area  1.66  times 
that  of  copper  to  have  an  equal  electrical  resistance  and 
transmit  a  given  amount  of  energy  with  equal  loss.  Or, 
since  the  cross-sectional  areas  of  round  wires  vary  as  the 
squares  of  their  diameters,  the  diameter  of  an  aluminum 
wire  must  be  1.28  times  greater  than  that  of  a  copper  wire 
of  the  same  length  to  possess  equal  conductivity. 

On  the  other  hand,  the  specific  gravity  of  copper  is  8.89, 
while  that  of  aluminum  is  but  2.7,  so  that  a  given  wire  of 
copper  weighs  3.3  times  as  much  as  an  aluminum  wire  of 
equal  volume.  Hence  a  copper  conductor  of  the  same 
length  and  resistance  as  an  aluminum  one  is  approximately 
twice  as  heavy.  It  is  quite  evident  that  reduction  by  one 
half  of  the  weight  on  poles,  insulators,  cross-arms,  etc., 


180     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

becomes  of  very  great  advantage  in  long  lines,  and  espe- 
cially when  the  transmission  line  is  projected  over  rough 
sections  of  country. 

It  is  also  found  that  the  vibration  of  transmission  lines 
in  heavy  winds,  which  tends  to  make  cross-arms,  pins,  and 
the  fastenings  of  conductors  work  loose,  is  somewhat  less 
with  aluminum  than  with  copper  conductors,  as  ordinarily 
strung,  on  account  of  the  smaller  weight  of  aluminum,  and  the 
greater  sag  between  poles  which  are  given  aluminum  lines. 

Since  a  pound  of  aluminum  made  into  a  conductor  of 
any  length  has  a  sectional  area  3.33  times  greater  than  an 
equal  weight  and  length  of  copper,  and  for  equal  resistance 
has  one  half  its  weight,  it  is  obvious  that  when  aluminum 
can  be  bought  at  a  lower  price  per  pound  than  twice  the 
cost  of  copper,  the  former  metal  is  the  cheaper  for  trans- 
mission purposes. 

As  compared  with  copper,  the  electrostatic  capacity  of 
aluminum  is  from  5  to  8  per  cent  greater,  depending  upon 
the  amount  of  energy  transmitted  and  the  length  of  the 
line.  (For  equivalent  conductors,  capacity  is  a  logarithmic 
function  of  diameter  divided  by  distance  apart.)  Aluminum, 
however,  possesses  several  disadvantages  which  make  it  ad- 
visable to  observe  considerable  precaution  in  the  use  of 
it  in  regions  where  adverse  climatic  conditions  prevail. 
Owing  to  its  larger  cross-sectional  area,  as  compared  with 
copper,  it  offers  a  larger  resisting  surface  to  wind  storms, 
which  if  not  actually  destructive  may  permanently  elongate 
it,  and  so  give  rise  to  dangerous  sags  in  the  line.  Its 
greater  diameter  also  affords  a  larger  surface  for  the  ac- 
cumulation of  ice,  which  on  account  of  the  low  ductility  of 
the  metal  may  cause  a  breakdown  in  the  line.  The  very 
high  coefficient  of  expansion  of  aluminum  with  change  of 


THE   TRANSMISSION    LINE  l8l 

temperature  is  also  a  very  objectionable  feature  in  regions 
subject  to  erratic  or  wide  fluctuations  in  temperature,  and 
renders  line-stringing  exceedingly  difficult. 

Aluminum  is  also  greatly  subject  to  electrolytic  cor- 
rosion, and  is  readily  attacked  by  the  fumes  from  chemical 
works,  especially  when  they  contain  sodium.  It  is  a 
highly  electro-positive  metal,  and  when  exposed  to  the 
atmosphere  in  contact  with  any  other  metal,  an  insidious 
electrolytic  action  ensues  in  which  the  electrolyte  is  the 
moisture  of  the  air  contaminated  with  chemical  impurities. 
This  property  of  the  metal  has  rendered  the  proper  con- 
struction of  joints  in  an  aluminum  transmission  line  a 
matter  of  extraordinary  difficulty. 

Most  of  the  breakdowns  and  consequent  dissatisfaction 
with  aluminum  as  a  conductor  are  due  to  a  disregard  of 
the  electrical  character  of  the  metal.  If  it  becomes  ab- 
solutely necessary  to  solder  the  joints  of  an  aluminum  line, 
or  to  use  a  joint  composed  of  aluminum  and  another  metal, 
the  joint  must  be  waterproofed  so  thoroughly  that  not  a 
particle  of  moisture  can  come  in  contact  with  the  metals 
composing  it.  The  usual  joint  employed  and  one  which 
obviates  all  difficulties  from  corrosion,  consists  of  an  oval 
aluminum  tube  (similar  to  the  Mclntire  joint),  about  ten 
inches  in  length,  which  is  twisted  some  three  or  more 
times  around  itself  after  the  ends  of  the  conductors  to  be 
united  have  been  introduced. 

An  objectionable  feature  of  aluminum  when  used  in 
small  sizes  is  the  low  fusing  point  of  the  metal.  It  melts 
at  1157°  F.,  while  copper  melts  at  1929°  F.,  and  wrought 
iron  at  2800°  F.  Hence  if  an  iron  or  copper  wire  falls 
across  an  aluminum  line,  the  latter  might  readily  be  melted 
in  two  by  the  current  flow  through  the  cross,  while  the 


182      LONG-DISTANCE   ELECTRIC   POWER  TRANSMISSION 

wire  causing  the  trouble  would  not  be  affected.  True,  this 
is  an  easy  method  of  eliminating  the  trouble,  but  at  the 
serious  expense  of  interrupting  the  service. 

As  regards  energy  losses,  there  is  but  little  difference 
between  the  two  metals,  the  advantage  being  in  favor  of 
copper.  As  regards  cost,  the  advantage  is  greatly  in  favor 
of  aluminum.  In  fact,  one  of  the  main  reasons  for  its  use, 
outside  of  the  physical  properties  enumerated,  is  the  com- 
parative cheapness  of  the  metal. 

Aluminum  is  used  as  an  aerial  conductor  only  in  the 
stranded  or  cable  form,  and  only  in  the  bare  form.  The 
solid  wire  shows  considerable  lack  of  uniformity  of  strength, 
even  in  the  same  sample,  and  breakdowns  in  lines  con- 
structed of  solid  metal  are  not  infrequent. 

When  copper  is  used  as  the  conducting  medium  for  high 
pressures,  it  is  always  in  the  form  of  bare,  medium  hard- 
drawn,  solid,  round  metal.  The  experience  in  American 
high-tension  practice  is  that  copper  wires  smaller  than  No. 
5  B.  &  S.  gauge  should  not  be  used  on  long-distance  lines. 

Relative  Weights  of  Metal  Required  for  Single- Phase 
Two-Phase,  and  Three-Phase  Circuits.  —  In  long-distance 
power  transmission,  a  problem  of  highest  importance  is  the 
determination  of  the  system  which  will  give  the  greatest 
efficiency  of  transmission  with  the  best  economy  of  ma- 
terial, and  which  at  the  same  time  will  be  thoroughly  reliable 
in  its  operation.  Application  is  made  of  the  general  law 
of  copper-conducting  circuits,  that  the  weight  of  copper  is 
inversely  proportional  to  the  square  of  the  voltage,  other 
things  being  equal. 

The  accompanying  diagram  (Fig.  85),  taken  from  Dr. 
C.  P.  Steinmetz's  classic  "  Alternating  Current  Phenom- 
ena," shows  the  relative  weights  of  copper  needed  for 


THE  TRANSMISSION   LINE 


183 


the  various  systems.  The  standard  chos.en  for  comparison 
is  the  single-phase  two-wire  system,  for  which  the  percent- 
age of  copper  required  is  100. 

Considering  first  the  single-phase    three-wire  system  : 
If  the  voltage  of  the  two-wire  system  is  e,  the  pressure  be- 

WIRING  CONNECTIONS  PERCENT.  DIAGrTMIH 


Single  Phase  ', 
2  Wire 


PER  CENT. 
COPPER 

100. 


I 


Single  Phase  I 
3  Wire        <~ 


Two  Phase 
4  Wire 


Two  Phase 
3  Wire 


Three  Phase 
3  Wire 


Three  Phase ihtJ^- 
4  Wire        ^ 

I1-1" 


31.6 


100. 


J14B.T 
1  72.9 


83.8 


Fig.  85 


4- 


A 

A 


tween  the  two  outside  conductors  is  2e.  But  since  the 
amount  of  copper  is  inversely  proportional  to  the  square  of 
the  voltage,  the  weight  of  copper  is  but  one  quarter  when  the 
neutral  conductor  has  no  cross-section,  or  when  the  system 
is  balanced,  thus  dispensing  with  a  neutral  return  conductor. 


184     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

When  the  cross-section  of  the  neutral  conductor  is  equal 
to  that  of  an  outside  conductor,  the  maximum  amount  of 
copper  required  for  a  single-phase  three-wire  system  is  37.5 
per  cent  of  that  required  by  a  two-wire  single-phase  system, 

When  the  neutral  wire  has  one  half  the  cross-section  of 
each  outside  conductor,  the  maximum  amount  of  copper  re- 
quired is  31.25%  of  that  of  the  standard  system.  When 
the  neutral  has  one  third  the  cross-section  of  the  outside 
wire,  the  amount  of  copper  needed  is  29. 1 5  per  cent  of 
the  standard  system. 

For  a  two-phase  four-wire  system,  which  is  the  equiva- 
lent of  two  single-phase  systems,  the  amount  of  copper 
required  is  the  same  as  that  needed  by  two  single-phase 
two-wire-  lines. 

When  a  two-phase  three-wire  system  is  used  the  deter- 
mination of  the  necessary  copper  is  more  complicated. 
When  a  conductor  of  full  cross-section  is  substituted  for 
two  of  the  leads  of  the  four-wire  system,  the  pressure 
between  the  two  outside  conductors  is  increased  to 
*^2~e  =  1.41  e,  e  being  the  voltage  bet  ween  the  conductors 
of  either  phase.  Hence  the  amount  of  copper  necessary 
will  differ  according  to  whether  the  basis  of  comparison  is 
the  maximum  permissible  potential  for  a  given  distribution 
or  the  minimum  potential  for  low-pressure  work. 

W7hen  insulation  stresses  or  other  causes  limit  the  high- 
est permissible  pressure  to  e,  thus  reducing  the  voltage 
between  the  other  leads  of  a  two-phase  three-wire  system 

e 
to  — r->  the  amount  of  copper  needed  is  145.7  of  tnat  °f 

the  standard  system.  When  limitations  of  working  po- 
tential do  not  hold,  the  basis  of  comparison  is  the  effective 
pressure  of  either  phase,  or  a  minimum  pressure  consider- 


THE   TRANSMISSION    LINE  185 

ation.  The  economy  in  copper  over  the  single-phase 
system  is,  under  such  conditions,  27  per  cent,  or  72.9 
of  the  copper  required  by  the  single-phase  standard  system. 

For  a  three-phase  three-wire  system  the  weight  of 
copper  necessary  for  any  definite  set  of  conditions  is  75 
per  cent  of  the  copper  required  by  the  standard  system. 

With  three-phase  systems,  the  comparison  of  relative 
weights  of  copper  is  easier  made  if  the  system  be  resolved 
into  a  number  of  single-phase  systems  corresponding  with 
the  number  of  phases. 

A  three-phase  system  is  made  up  of  three  single  wires 
with  no  return  conductor,  since  the  maximum  current  to 
and  from  the  middle  is  zero.  The  voltage  of  the  line  is  e, 
and  the  pressure  between  any  wire  and  the  neutral  point 

e 
of  the  system  is  — p- 

Vs 

For  a  three-phase  four-wire  system  with  a  neutral  of 
full  cross-section,  the  weight  of  copper  necessary  is  33^ 
per  cent  of  the  standard  single-phase  system.  If  the  cross- 
section  of  the  neutral  wire  be  made  one  half  that  of  the 
main  wires,  the  weight  of  copper  necessary  is  29.15  per 
cent  of  the  standard  system.  A  system  of  this  \indis 
only  used  for  distribution  from  transformer  secondaries  ; 
hence  it  is  compared  with  other  systems  only  on  the  basis 
of  equality  between  phases  of  minimum  voltage. 

The  choice  between  transmission  systems  for  long-dis- 
tance lines  is  practically  confined  to  the  two-phase  three- 
wire  and  the  three-phase  three-wire  systems.  The 
question  as  to  which  is  preferable  is  still  a  mooted  one. 
For  all-round  service  the  three-phase  three-wire  system 
offers  the  advantages  of  simplicity  in  line  construction, 
greater  economy  in  copper  and  higher  efficiency  of  trans- 


l86     LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 


mission.  But  the  two-phase  three-wire  system  gives  on 
the  whole  a  better  line  regulation  and  is  much  more 
reliable  for  loads  made  up  entirely  of  motors. 

The  majority  of  long-distance  power  transmission  com- 
panies in  the  United  States  employ  the  three-phase 
three- wire  system  for  transmitting  the  energy,  and  the 
two-phase  four -wire  system  from  step-down  transformer 
secondaries,  for  distribution,  with  mixed  loads. 

The  accompanying  tables  from  Steinmetz's  "  Alternating 
Current  Phenomena  "  show  the  copper  efficiencies  of  the 
various  systems  on  the  basis  of  maximum  and  minimum 
differences  of  pressure. 

Amount  of  copper  required  for   transmission  at  a  given  loss,    based  on 
minimum  potential. 


System. 

No.  of  Wires 

Per  cent 
Copper 

Single-phase  

2 

100. 

Single-phase 

3 

37  5 

Two-phase,  common  return  

3 

72.9 

Two-phase  .                                                    .... 

4 

100. 

Three-phase    

3 

75. 

Three-phase,  neutral  full  section. 

4 

33  3 

Three-phase,  neutral  one-half  section  

4 

29.17 

Amount  of  copper  required  for  transmission  at  a  given  loss,  based  on  maxi- 
mum difference  of  potential. 


System. 

No.  of  Wires 

Per  cent 
Copper 

Single-phase.    

2 

i  on 

Two-phase,  witli  common  return  

3 

14^  7 

Two-phase  

4 

ion 

Three-phase  .          .        

3 

75 

Direct  Current  

2 

50. 

THE   TRANSMISSION   LINE  l8/ 

Transmission  Line  Poles.  —  Poles  used  for  supporting 
long-distance  transmission  lines  are  of  cedar,  chestnut, 
pine,  redwood,  fir,  or  spruce.  The  use  of  a  particular  wood 
for  a  pole  line  depends  upon  the  expenditure  allowed  for 
line  construction,  the  factor  of  safety  desired,  and  the  prev- 
alence of  a  particular  and  readily  obtained  wood  in  the 
section  of  country  through  which  the  line  passes. 

Cedar  poles  are  in  extensive  use,  owing  to  their  great 
durability,  but  are  seldom  used  in  lengths  greater  than  50 
to  5  5  feet,  since  cedar  poles  of  greater  height  and  having 
suitable  dimensions  are  difficult  to  obtain,  and  if  obtain- 
able their  cost  is  prohibitive.  The  brittleness  of  the  wood 
also  precludes  its  use  on  lines  which  must  be  strung  at 
considerable  distances  above  the  ground. 

On  account  of  its  cheapness  and  abundance  pine  is  more 
widely  used  for  line  support  than  other  wood.  Although 
not  near  so  durable  nor  stout  as  some  of  the  other  woods, 
such  as  cedar  or  redwood,  its  cheapness  and  the  ease  of 
obtaining  it  compensate  in  many  cases  for  these  disadvan- 
tages. 

Along  many  of  the  Western  transmission  lines  which 
traverse  mountainous  regions  the  most  abundant  woods  are 
several  varieties  of  fir  and  spruce,  which  are  extensively 
used  in  pole  lines  on  account  of  their  straightness  and 
toughness  and  the  readiness  with  which  they  can  be  obtained 
in  the  proper  sizes. 

In  California  transmission  circuits,  considerable  redwood 
is  used,  which  is  always  of  rectangular  section,  because  of 
the  great  size  of  the  redwood  tree  and  the  necessity  of  cut- 
ting it  up  into  sections  for  poles. 

It  is  advisable  to  treat  poles  of  soft  woods  such  as  spruce 
and  pine  with  some  kind  of  preservative  before  they  are 


188       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

set  in  the  ground,  but  owing  to  the  added  expense  this 
treatment  is  seldom  given  to  poles  for  high-tension  lines. 
Some  Western  transmission  companies,  however,  apply  hot 
tar  or  carbolineum  to  the  butts  of  the  poles  or  bore  into 
the  centers  and  give  them  fillings  of  the  latter  compound. 

While  the  sizes  of  poles  used  in  long-distance  transmis- 
sion lines  vary  considerably  with  the  special  conditions 
which  must  be  met,  it  may  be  said  in  general  that  the 
length  is  never  under  30  feet  and  the  diameter  at  the  top 
is  never  less  than  7  inches.  In  the  mountainous  sections 
of  the  West,  the  length  of  pole  used  is  seldom  greater  than 
30  or  35  feet,  with  a  top  diameter  of  8  inches  ;  but  on 
level  stretches  the  poles  are  five  or  more  feet  higher  as  a 
precaution  against  mischievous  attempts  to  throw  obstruc- 
tions over  the  line.  The  average  length  of  the  poles  for 
high-tension  transmission  lines  is  about  40  feet,  with  a  butt 
diameter  of  10  inches  and  tapering  to  8|  inches  at  the  top. 
The  length  of  the  poles  should  be  so  proportioned  to  the 
contour  of  the  region  that  the  line  may  be  laid  out  without 
any  abrupt  changes  in  its  level.  In  crossing  other  pole 
lines,  such  as  telegraph  and  telephone  lines,  it  is  customary 
to  use  poles  of  sufficient  height  to  carry  the  high-tension 
line  at  a  safe  distance  above  the  other  line,  in  order  to  re- 
duce the  liability  to  crosses. 

Poles  are  generally  set  in  the  ground  to  the  following 
depths : 

Height  of  Pole  Depth  of  Setting 

35  to  45  feet  5    to  6  feet 

50  «  55    «  6£  «    7£  « 

60  "  80    "  ;£  «   8£  " 

The  length  of  life  of  poles  varies  quite  markedly,  being 
dependent  upon  the  character  of  the  wood,  the  kind  of  soil 


THE  TRANSMISSION   LINE  189 

in  which  it  is  set,  and  the  climatic  conditions  of  the  region. 
The  life  of  a  cedar  pole  varies  from  fifteen  to  twenty  years 
and  not  infrequently  they  last  thirty  years.  The  average 
length  of  life  of  a  chestnut  pole  is  twelve  years,  while 
that  of  a  pine  pole  is  from  six  to  ten  years.  Redwood  and 
fir  poles  last  almost  as  long  as  cedar. 

Construction  of  Pole  Lines.  —  The  construction  of  the 
pole  line  must  be  carried  out  with  scientific  accuracy  in 
order  to  obtain  the  highest  efficiency  of  service  and  freedom 
from  line  troubles.  Hence  in  most  pole-line  construction 
the  line  should  not  only  be  staked  out  by  a  surveyor,  but 
the  poles  should  be  set  with  plumb  bobs,  and  the  construc- 
tion chief  should  use  a  thermometer  and  a  set  of  curves  to 
determine  the  correct  sag  to  allow  the  wires  at  different 
points  along  the  route.  When  the  section  of  country 
through  which  the  line  passes  is  smooth  and  level,  and 
where  the  soil  is  of  a  character  which  will  hold  the  pole 
rigidly  in  position,  no  especial  difficulties  are  encountered 
in  the  erection  of  poles.  Under  such  conditions  the  points 
for  the  holes  are  carefully  located  and  the  excavations  made 
to  the  proper  depth.  The  poles  having  been  distributed 
at  the  holes,  each  pole  is  set  in  position  by  from  four  to 
ten  men,  depending  on  its  dimensions  ;  the  earth  is  firmly 
tamped  around  its  butt  and  the  task  is  finished. 

In  case  the  line  must  traverse  marshy  or  "made  "  ground, 
it  becomes  essential  to  put  a  concrete  mixture  around  the 
pole,  composed  in  some  instances  of  one  part  of  cement, 
three  parts  of  sand,  and  five  parts  of  broken  stone. 

Where  the  pole  must  be  set  in  rock,  the  butt  should  be 
hewn  to  fit  a  suitable  iron  shoe,  which  is  rigidly  bolted  to 
the  rock.  To  prevent  corrosion  of  this  shoe,  it  should  be 
painted  on  the  inside  with  white  lead  before  the  pole  is  in- 


1 90    LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

serted.  The  outside  of  the  shoe  should  be  left  smooth,  and 
hydraulic  cement  spread  over  the  top  surface  of  the  rock 
on  which  the  shoe  is  set. 

It  is  the  general  rule  in  Western  practice  to  place  two 
poles  together  whenever  an  angle  is  made  in  the  line,  so 
that  the  strain  will  be  equally  divided  between  the  two. 

The  absence  of  guy  wires  in  pole-line  construction  is 
quite  common  on  the  Pacific  coast  ;  wooden  struts  are  in 
more  general  use.  Those  usually  employed  average  6 
inches  by  6  inches,  and  are  attached  to  a  "dead  man" 
buried  about  5  or  6  feet  in  the  ground.  In  cases  where 
it  becomes  imperative  to  use  a  guy,  the  strut  is  sometimes 
used  as  an  anchor,  or  else  a  piece  of  timber  about  6  inches 
by  6  inches  by  20  feet  long  is  inserted  in  the  guy  to  serve 
as  a  sort  of  strain  insulator. 

Transmission  lines  operating  at  high  potentials  are  gen- 
erally run  over  a  private  right  of  way,  varying  with  the 
conditions  from  60  to  300  feet  in  width.  Where  the  line 
goes  through  forests,  the  trees  on  each  side  of  it  must  be 
cleared  away  to  a  distance  sufficiently  great  to  prevent 
trees  felled  by  wind  or  lumbermen  from  falling  across  the 
line  wires. 

Since  the  majority  of  high-tension  lines  furnish  power  to 
enterprises  to  which  an  interruption  of  the  service  would 
entail  serious  loss  and  inconvenience,  it  is  generally  custom- 
ary to  install  the  lines  in  duplicate.  The  first  practice  was 
to  install  both  circuits  on  the  same  pole  line,  but  induct- 
ance and  short-circuit  troubles  render  it  imperative  to  con- 
struct a  separate  and  similar  transmission  line. 

Although  the  use  of  duplicate  lines  insures  continuous 
service,  it  is  found  that  unless  the  most  improved  form  of 
oil  switches  are  used  in  the  plant  that  even  the  brief  shut- 


THE   TRANSMISSION    LINE  IQI 

downs  occasioned  by  switching  from  the  defective  to  the 
duplicate  circuit  causes  some  dissatisfaction.  This  is 
largely  due  to  the  fact  that  the  opening  of  the  line  by  or- 
dinary types  of  switches  is  rather  a  slow  process,  and  is  at> 
tended  with  considerable  hazard,  as  surges  of  a  destructive 
character  may  follow. 

Stresses  on  Pob-Lin3s.  —  Stresses  on  pole  lines  are  made 
up  of  the  following  components:  (i)  Weight  of  conductors 
and  the  force  acting  downward  due  to  conductor  tension. 
Since  the  factor  of  safety  of  a  pole  is  usually  about  90  or 
above  this  first  component  is  negligible.  (2)  Bending  mo- 
ment caused  by  the  pull  of  the  conductors  when  angles  or 
turns  are  made  in  the  line.  (3)  Wind  stress  on  conductors 
and  poles.  (4)  Wind  stress  *and  the  weight  of  ice  on  the 
line. 

A  fairly  accurate  value  of  the  bending  moment  may  be 
obtained  by  the  following  formula  : 


where    J/6  =  bending  moment. 

Ca=area  of  the  pole  at  the  ground. 
S=  strength  of  pole  per  unit  cross-section. 
I?  =  radius  at  the  ground. 
D  =  distance  between  ground  and  the  center  of  pressure. 

The  bending  moment  caused  by  a  turn  or  angle  is 

<A 
2  77cos  —  ' 

2 

where  T  is  the  tension  and  <J>  the  angle  between  the  con- 
ductors at  the  turn. 

To  find  approximately  the  wind  pressure  on  a  line,  the 
following  formula  may  be  used  : 
/>=o.o5 


192    LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 
in  which 


pressure  per  square  foot. 
//„  =  average  diameter  of  pole. 
^•=free  length  of  pole  above  ground. 
Sc  =  pressure  on  conductors,  per  se. 

To  find  the  stress  due  to  wind  and  ice  : 

(ioo)2  X  weight  of  conductors  per  foot 
%d 

Cross-Arms  —  Methods  of  Attaching.  —  Cross-arms  used 
in  high-tension  practice  are  made  of  cedar,  chestnut,  oak, 
red  and  yellow  pine,  and  redwood.  They  are  usually 
rounded  or  chamfered  at  the  side-top  to  prevent  the  ac- 
cumulation of  water  in  the  grain  of  the  wood. 

Cross-arms  vary  in  length  and  cross-section  with  the 
conditions  which  must  be  met,  such  as  the  weight  of  the 
conductors,  the  distance  apart  of  the  conductors,  the  size 
of  insulator  pins  and  insulators,  and  the  wind  and  ice 
stresses  which  they  must  withstand. 

No  special  rule  applies  for  the  dimensions  of  cross-arms 
for  a  given  transmission  voltage.  It  may  be  said  in  gen- 
eral that  for  pressures  ranging  from  10,000  to  20,000  volts 
the  length  of  cross-arm  varies  from  four  and  a  half  to  eight 
feet  depending  upon  the  distance  between  wires. 

Fig.  86  shows  the  standard  10,000  volt  cross-arm  used  by 
the  California  Edison  Company,  and  Fig.  87  shows  the 
dimensions  of  the  cross-arm  used  on  the  3  3,000  volt  pole 
line  of  the  same  company  from  Santa  Ana  to  Los  Angeles. 

Cross-arms  in  the  latest  transmission  lines  in  the  West 
are  made  of  carefully  selected  kiln-dried  Oregon  pine, 
6  inches  by  6  inches,  and  of  lengths  depending  upon  the 
distance  between  wires. 

It  has  now  become  quite  general  practice  in  the  West  to 


THE   TRANSMISSION   LINE 


193 


give  cross-arms  one  or  the  other  of  two  kinds  of  treatment 
before  they  are  attached  to  the  poles.  In  the  first  method, 
after  being  thoroughly  kiln-dried,  they  are  placed  in  an 


Fig.  86.    Cross- Arm  Used  on  a  10,000  Volt  Line 

inclosed  boiler  filled  with  asphaltum  oil,  which  is  main- 
tained at  a  temperature  of  about  220°  F.  for  several  hours. 
This  serves  two  purposes :  It  preserves  the  wood,  and  it 


fi 


Fig.  87.1  Cross-Arm  Used  on  a  33,000  Volt  Line 

increases  the  insulation  of  the  cross-arm  and  pole  top  and 
tends  to  prevent  the  burning  of  the  arm  when  an  insulator 


IQ4     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

pin  proves  defective,  or  when  a  short  circuit  occurs  on  the 
line. 

The  second  mode  of  treatment  consists  in  boiling  the 
cross-arm  thoroughly  in  linseed  oil. 

Cross-arms  are  fastened  to  poles  either  by  means  of  lag 
screws  or  by  through  bolts  of  from  five  eighths  inch  to 
three  fourths  inch  diameter,  fitted  with  cast-iron  washers 
about  3  inches  in  diameter,  under  both  head  and  nut.  The 
use  of  through  bolts  is  somewhat  objectionable  for  the 
reason  that  when  a  cross-arm  must  be  replaced  it  is  fre- 
quently necessary  to  use  a  drift  pin  to  drive  out  the  rusted 
bolt. 

Cross-arms  for  very  long  pole  lines  being  necessarily  very 
heavy  and  lengthy  require  to  be  stoutly  braced.  For  this 
purpose  single-piece  angle  iron  is  quite  commonly  em- 
ployed. Fig.  88  shows  a  bracing  frequently  employed. 

The  advantage  of  a  single-piece  brace  lies  in  the  fact  that 
if  one  of  the  line  conductors  should  slip  from  its  insulator 
down  on  the  cross-arm,  and  thus  be  burned  in  two  at  the 
middle,  the  two  ends  supported  by  the  angle-iron  brace 
may  be  preserved  intact  without  interrupting  the  service. 

In  order  to  overcome  the  effect  of  line  strains  and  windage, 
cross-arms  are  sometimes  braced  on  both  sides  of  the  pole. 
As  a  precaution  against  the  splitting  of  cross-arms,  when 
severe  stresses  are  brought  to  bear  against  the  pins,  car- 
riage bolts  one  half  inch  in  diameter  are  sometimes  mounted 
at  a  distance  of  3  inches  from  the  pin,  and  approximately 
2  inches  from  the  top  of  the  cross-arm.  A  series  of  tests 
conducted  by  a  California  transmission  company  showed 
that  cross-arms  could  be  split  without  these  bolts  by  a  force 
of  1,200  pounds,  whereas  with  the  bolts  in  place  the  pin 
split  at  the  shoulder  under  a  force  of  2,200  pounds, 


THE   TRANSMISSION    LINE 


195 


On  straight  runs  of  considerable  length,  cross-arms  are 
set  to  face  each  other  alternately  on  adjacent  poles,  and  are 
placed  back  to  back  on  the  next  two  poles.  This  method 
of  construction  obviates  the  danger  of  a  cross-arm  being 
wrenched  off  if  a  pole  should  break,  or  if  a  stretch  of  line 
is  broken. 

Cross-arms  should  be  doubled  at  all  long  stretches  and 
corners,  and  whenever  the  line  is  dead-ended.  To  accom- 


Usual  Method  of  Bracing  Cross-Arms 


plish  this,  a  spacing  block  is  used  at  each  end  of  the  cross- 
arm,  and  the  arm  is  fastened  at  the  ends  by  bolts  through 
the  spacing  blocks. 

Methods  of  Prcs^rvinj  Wood.  —  The  principal  causes  of 
the  decay  of  poles  and  cross-arms  are  the  fermentation  of 
the  sap  and  the  alternate  wetting  and  drying  to  which  they 


196      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

are  subjected  ;  the  latter  trouble  makes  the  wood  crack 
and  split  and  invites  early  decay  on  account  of  the  settling 
of  water  in  the  grain  of  the  timber. 

Six  methods  are  employed  for  the  preservation  of  wood, 
viz.  :  Creosoting,  vulcanizing,  burnettizing,  kyanizing,  car- 
bolining,  and  smearing  with  pitch  or  tar. 

In  creosoting  poles,  they  are  loaded  on  a  flat  car,  sep- 
arated by  laths  or  strips  of  wood ;  the  cars  are  then 
run  into  an  immense  cylinder  fitted  with  air-tight  iron 
doors ;  with  the  doors  closed,  live  steam  at  a  temperature 
of  about  250°  F.  is  turned  in  the  cylinder  until  the  heat 
causes  the  albumen  of  the  sap  to  coagulate.  The  sap  is 
then  extracted  by  forming  a  vacuum  in  the  cylinder. 
When  this  is  accomplished  coal  tar  or  some  variety  of  dead 
oil  is  forced  into  the  cylinder  under  a  pressure  of  about  125 
pounds  per  square  inch.  The  quantity  of  oil  used  varies 
with  the  kind  of  timber  and  ranges  from  1 2  to  24  pounds 
per  cubic  foot. 

Vulcanizing  is  carried  out  by  subjecting  the  wood  to  a 
temperature  of  several  hundred  degrees  Fahrenheit  in 
closed  chambers,  under  a  pressure  of  150  to  200  pounds  per 
square  inch.  Usually  heating  for  about  a  half  day  suffices. 
The  heat  so  alters  the  character  of  the  sap  that  no  fermen- 
tation ensues. 

Burnettizing  is  accomplished  by  forcing  a  i  to  3  per 
cent  solution  of  chloride  of  zinc  into  the  pores  of  the 
wood.  But  since  this  is  easily  washed  out  in  several 
methods,  as  for  instance  the  Thilmay  process,  it  is  aimed 
to  prevent  this  by  the  use  of  two  different  chemical  solu- 
tions which  react  to  form  an  insoluble  salt.  In  the  Thil- 
may process  sulphate  of  zinc  is  first  injected,  followed  by 
barium  chloride.  The  reaction  which  follows  results  in 


THE   TRANSMISSION    LINE  1 97 

zinc  chloride  and  barium  sulphate,  which  latter  compound 
is  insoluble. 

Kyanizing  is  carried  out  by  immersing  the  wood  for 
some  time  in  a  3  per  cent  solution  of  bichloride  of 
mercury. 

-The  carbolining  process  is  effected  either  by  soaking  the 
timber  in  carbolineum  oil  at  200°  to  300°  F.,  or  else  by  in- 
jecting the  hot  oil  into  the  center  of  the  material  by  boring 
small  holes  into  it.  This  method  of  preservation  is  more 
generally  employed  in  Western  pole-line  construction  than 
any  other. 

""  Smearing  the  butts  of  poles  with  tar  or  pitch  is  quite 
commonly  resorted  to,  but  it  is  harmful  unless  the  wood 
is  well  seasoned.  When  applied  to  a  wet  or  unseasoned 
pole,  tar  or  pitch  promotes  decay,  as  it  seals  the  pores 
of  the  wood  and  accelerates  the  fermentation  of  the  sap. 

Steel-Supporting  Structures  for  Transmission  Lines.  — 
The  peculiar  troubles  to  which  pole  lines  are  liable,  such  as 
damage  by  wind  storms,  burning  of  cross-arms,  necessity  of 
constant  replacing  on  account  of  decay,  not  excepting  the 
need  of  frequent  patrolling,  have  prompted  considerable 
discussion  relative  to  the  advisability  of  using  steel  towers 
instead  of  poles  to  carry  long-distance  high-tension  circuits. 
Fig.  89  shows  a  type  of  steel  tower  used  in  the  seventy-five 
mile  power  transmission  circuit  of  the  Ontario  Power  Com- 
pany, from  Niagara  Falls  to  Montreal.  The  proposition 
offers  many  advantages  as  a  means  of  decreasing  the  num- 
ber of  breakdowns  and  the  general  maintenance  of  lines, 
although  the  initial  cost  of  such  construction  is  somewhat 
greater  than  with  poles. 

It  has  been  proposed  to  use  steel  towers  about  ninety 
feet  high  and  about  1,000  feet  apart,  the  wires  to  be  sus- 


198       LONG-DISTANCE  ELECTRIC   POWER  TRANSMISSION 

pended  from  tower  to  tower  and  about  nine  feet  distant 
from  each  other. 

As  regards  the  advantages  and  disadvantages  of  steel 


Fig.  89.     Type  of  Steel  Tower  Used  in  Niagara  Falls  —  Montreal  Transmission 

structures  and  poles  for  long-distance  line  construction  the 
following  comparison  may  be  made: 

At  least  fifty  poles  per  mile  are  required,  necessitating 
the  use  of  150  insulators  per  mile  for  a  three-wire  circuit. 
With  steel  towers,  which  can  be  spaced  500  feet  apart  or 
ten  spans  per  mile,  the  number  of  insulators  required  is 
about  thirty  per  mile.  This  large  reduction  in  the  number 


THE   TRANSMISSION    LINE  199 

of  insulators  makes  up  for  the  difference  in  cost  of  instal- 
lation, even  when  poles  are  cheap. 

Most  of  the  trouble  on  high-tension  lines  is  due  to  break- 
age or  failure  of  insulators.  From  the  figures  cited  as  to 
the  Guanajuato  towers  (pages  200-201)  it  is  evident  that 
steel  supporting  structures  reduce  such  maintenance  nearly 
80  per  cent. 

Wood  poles  are  liable  to  damage  by  lightning,  prairie 
and  incendiary  fires,  and  in  remote  districts  may  be  hacked 
to  pieces  by  the  natives  for  fuel. 

Few  climates  allow  wood  poles  to  remain  safe  at  the 
ground  line  more  than  five  years.  In  some  semi-tropical 
and  tropical  climates  eighteen  months  measure  the  life  of 
a  wood  pole,  thereby  entailing  constant  expense  for  main- 
tenance. With  steel-supporting  structures  this  expense  is 
obviated. 

Lightning  does  not  damage  steel  towers,  and  with 
proper  protective  devices,  the  use  of  which  is  impossible 
on  pole  lines,  the  insulators  and  conductors  may  be  pro- 
jected so  as  to  reduce  the  lightning  damage  to  a  minimum  ; 
this  damage  in  mountainous  regions  and  the  tropics  is 
one  of  the  heaviest  items  in  the  maintenance  account  of  a 
pole  line. 

The  following  prices  are  current  on  steel  towers 
(Aermotor  Company)  : 

40  ft.  towers  weighing  approximately  1,400  Ibs.  $46.00 

5oft.       "              «                     "  i, 730  Ibs.  57.00 

60  ft.       "              "                     "  2,000  Ibs.  68.00 

70  ft.      "             "                    "  2,575  lbs-  84-°° 

80  ft.       "             "                    "  2,900  lbs.  102.00 

90  ft.       "             "                    "  3>5°°  lbs.  123.00 


2OO     LONG-DISTANCE    ELECTRIC    POWER  TRANSMISSION 

The  approximate  cost  per  mile  of  constructing  a  high- 
tension  circuit  with  a  pole  line  and  with  steel  towers  is  as 
follows  : 

53  wooden  poles,  35  ft.  with  cross-arms  and 

pins,  at  $6.00  each  $318.00 

Erection,  $1.20  each  63.60 

3  x  53  insulators  at  $1.50  each  238.50 


$620.10 
9  steel  towers,    45    ft.    with    cross-arms    and 

pins,  at  $60.00  each  $540.00 

Assembling  and  erecting  at  $7.00  each  63.00 

3X9  insulators  at  $1.50  each  40.50 


$643.50 

In  Mexico  several  long-distance  lines  have  been  pro- 
jected in  which  the  entire  circuits  are  to  be  supported  on 
steel  structures.  Fig.  90  shows  the  type  of  tower  used  on 
the  no  mile,  60,000  volt  transmission  of  the  Guanajuato 
Power  and  Electric  Company,  and  built  by  the  Aermotor 
Company,  of  Chicago,  111.  Fig.  91  shows  the  method  of 
erecting  the  tower.  The  towers  employed  on  this  line  are 
uniformly  40  feet  in  height,  and  for  particular  locations 
were  provided  with  20  foot  extensions  to  permit  the 
stringing  of  the  conductors  60  feet  above  the  earth.  The 
weight  of  the  tower  is  approximately  1,500  pounds. 

The  towers  are  spaced  440  feet  apart,  making  twelve 
spans  per  mile,  and  carry  conductors  about  -f^  inch  in 
diameter,  with  17  or  18  feet  sag  between  insulators.  The 
side  strain  impressed  upon  the  insulators,  should  the 
conductor  break  between  supports,  would  be  about  900 
pounds  if  no  slippage  occurred  at  the  insulator. 


THE   TRANSMISSION    LINE 


201 


It  was  found  by  actual  test  that  the  extra  heavy  pipe 
which  extends  six  feet  above  the  top  of  the  tower  (Fig.  90) 
and  has  attached 
to  it  a  cast-iron  in- 
sulator pin,  stood 
the    same    press- 
ure, 900  pounds, 
without     being 
bent    beyond    its 
elastic  limit. 

The  cross-arms, 
which  are  made  of 
two  4  inch  chan- 
nel irons,  weigh- 
ing 5 1  pounds  per 
foot,  clamp  to  the 
pipe  immediately 
above  the  apex 
of  the  tower,  and 
are  bolted  to  the 
two  side  insulator 
pins. 

The  maximum 
side  strain  which 
can  be  impressed 
upon  a  tower, 
should  three  wires 
break  on  one  side, 
is  2,700  pounds. 
The  tower  itself,  properly  anchored,  safely  stood  a  strain  of 
2,500  pounds,  which  gives  it  some  excess  in  strength  over 
that  of  the  conductor  connections. 


Fig.  90.    Type  of  Steel  Tower  Used  on  a  Mexican 
Long-Distance  Line 


202     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

The  tower  is  put  together  with  bolts,  clamps,  etc.,  and 
is  assembled  on  the  site.  All  parts  are  thoroughly  gal- 
vanized. A  set  of  ladder  steps  to  attach  to  one  corner 
post  of  the  tower  is  provided  to  enable  linemen  to 
ascend  the  structure,  and  also  a  small  platform  near  the 
apex  to  form  a  support  for  linemen  when  putting  on 
insulators. 


Fig.  91.     Method  of  Erecting  Steel  Tower  Shown  in  Fig.  90 

The  anchorage  of  the  towers  consists  of  steel  anchor 
posts  6  feet  in  length,  with  a  stout  cross-piece  on  the 
higher  towers.  These  anchor  posts  were  set  firmly  in  the 
ground  and  weighted  with  rough  stone  and  rubble,  thus 
forming  a  secure  and  solid  foundation  for  the  structure. 
The  cost  of  the  towers,  including  cross-arms  and  insulator 
pins,  was  $53  each. 

Fig.  92  shows  a  twin-type  steel  tower  designed  to  cftrry 
two  high-tension  three-phase  circuits. 


THE   TRANSMISSION    LINE 


203 


Kinds  of  Insulator  Pins.  —  Pins  for  carrying  high-tension 
insulators  are  either  wooden  or  metallic.  Wooden  pins 
arfe  more  extensively  employed  at  the  present  time,  but 
are  being  gradually  displaced  by  iron  pins  on  account  of 
the  many  points  of  advantage 
which  the  latter  possess. 
Wooden  pins  are  made  of 
chestnut,  oak,  eucalyptus,  or 
locust.  In  California  redwood 
pins  are  in  quite  general  use, 
but  locust  and  eucalyptus  offer 
the  largest  number  of  points  of 
superiority. 

Locust  is  the  toughest  and 
most  lasting  of  woods,  but  is 
harder  to  obtain  and  much 
more  expensive  than  some 
other  varieties  of  timber.  Oak 
pins  when  properly  propor- 
tioned and  carefully  treated 
have  given  excellent  satisfac- 
tion, but  some  experience  has 
shown  that  they  have  a  ten- 
dency to  decay  in  a  few  years 
and  break  off  at  the  shoulder. 

On  the  Pacific  coast  euca- 
lyptus wood  is  almost  entirely 
used  for  insulator  pins  on  account  of  its  immunity  against 
the  attacks  of  worms  and  insects.  These  pins  are  given 
the  following  treatment  before  they  are  put  into  use : 
The  wood  is  first  cut  into  sticks  about  3  inches  square, 
which  are  then  immersed  in  boiling  water  for  about  a  day. 


Fig.  92.    Twin-Type  Tower  for  Two 
Three-Phase  Circuits 


204       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

After  this  preliminary  treatment  they  are  air  dried  for 
several  months  before  being  cut  into  the  desired  sizes  for 
pins.  Before  being  mounted  on  the  cross-arm  they  are 
boiled  for  several  hours  in  linseed  oil,  at  a  temperature  of 
about  210°  F.  (In  the  best  practice  wooden  pins  are  al- 
ways boiled  in  paraffine  or  linseed  oil  before  being  put  into 
use.) 

Holes  for  wooden  pins  average  2^  inches  in  diameter 
and  5  inches  deep.  In  general,  holes  of  these  dimensions 
leave  a  margin  of  about  I  inch  of  solid  wood  in  the  cross- 
arm  on  each  side  of  the  hole. 

One  of  the  principal  objections  to  wooden  pins  is  the  lia- 
bility to  become  charred  or  to  be  burnt  out  entirely  by 
leakage  currents  over  the  insulator.  Burning  generally 
takes  place  at  the  thread  of  the  pin.  In  some  transmis- 
sion lines,  trouble  has  been  experienced  by  the  current  arc- 
ing from  the  insulators  to  the  pins,  and  even  crossing  to 
cross-arms  and  pole  tops,  and  forming,  supposedly,  nitric 
acid.  The  elements  for  the  hydrogen  and  oxygen  of  the 
acid  are  present  in  water  which  settles  on  the  wood,  while 
the  nitrogen  comes  from  the  air.  The  acid  thus  formed 
acts  on  the  wood  and  makes  it  quite  pulpy.  Since  nitric 
acid  is  also  a  splendid  electrical  conductor  the  tendency  of 
the  current  to  strike  from  insulator  to  pin  is  greatly  in- 
creased ;  and  hence  in  time  the  thread  of  the  pin  and  other 
parts  become  charred  and  finally  break  off,  or  burn  out 
entirely. 

It  is  supposed  that  burning  or  charring  of  pins  at  the 
threads  is  due  to  the  high  resistance  of  the  pin  at  this 
point,  which  results  in  the  evolution  of  a  high  temperature 
by  the  leakage  current  from  the  insulator.  At  the 
lower  part  burning  seldom  occurs,  as  the  accumulation  of 


THE   TRANSMISSION   LINE 


205 


dust  and  organic  matter  affords  a  fairly  good  path  for  the 

current. 

Another  serious  drawback  in  the 

use   of   wooden    pins   is   that   a  de- 
fective insulator,  or  a  breakdown  of 

an   insulator,   usually  results  in  the 

complete  destruction  of  the  pin  and 

not  infrequently  in  the   burning  of 

the  cross-arm. 

Metallic  pins  are  generally  made 

of  wrought  iron,  and  are  constructed 

with    either    wooden  screw    threads 

and    porcelain    bases,    or    else   with 

wooden  tops  and  iron  bases,  or  with 

wood    tops    and    wood    bases.     The 

pin  proper,  or  bolt,  which  holds  the 

insulator  in  position  varies  in  dimen- 
sions from  one  half  inch 

by  i  o  inches  for  medium-sized  insulators,  up  to 
five  eighths  inch  by  1 1  inches  for  very  high 
pressures  and  heavy  insulators. 

Fig.  93  shows  a  Locke  iron  pin  with  a  porce- 
lain base,  and  Fig.  94  shows  the  same  pin  with 
an  all  wood  top. 

Metallic  pins  possess  the  following  advan- 
tages over  wooden  pins  :  Greater  mechanical 
strength,  greater  durability,  less  liability  to 
cause  a  breakdown  in  the  line  when  an  insu- 
lator proves  defective. 

Kinds  of  Insulators.  —  Advantages  and  Dis- 
advantages of  Glass  and  Porcelain. — Insulators 

for  high-tension  lines  are  of  either  glass  or  porcelain,  or 


Fig.  93.     Iron  Insulator  Pin 
with  Porcelain  Base 


Fig.  94.  Iron 
Pin   with 
Wood  Top 


206    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

a  combination  of  the  two.  They  differ  widely  from  those 
used  in  low-tension  practice,  the  essential  points  of  dif- 
ference being  a  stouter  mechanical  construction  and  special 
shapes  and  constructional  features  employed  to  enhance 
the  insulating  properties.  High-tension  insulators  require 
to  be  of  larger  diameter  than  low-tension  ones  for  the 
reason  that  the  striking  distance  through  the  air  varies 
from  3.5  to  6.5  inches,  so  that  wide  gaps  must  be  provided 
between  the  circuit  wires  and  all  extraneous  objects.  The 
"creeping  distance"  allowed  the  current  also  has  to  be 
appreciable. 

At  the  present  time  the  ideal  insulator  for  high-tension 
work  does  not  exist.  Some  insulators  are  strong  mechani- 
cally and  weak  electrically,  and  vice  versa.  For  mechani- 
cal strength,  high  insulating  properties,  and  the  greatest 
degree  of  reliability  under  all  conditions  of  operation,  the 
solid  porcelain  insulator  is  preeminently  superior  to  any 
other  form  that  is  now  used. 

In  point  of  mechanical  strength  porcelain  of  the  best 
grade  possesses  nearly  double  the  strength  of  the  best  glass 
obtainable,  as  can  be  demonstrated  by  letting  a  steel  ball 
fall  from  a  given  distance  on  insulators  made  of  the  two 
materials. 

In  point  of  insulating  properties  porcelain  is  fully  equal 
to  the  best  glass,  and  its  non-hygroscopic  character  insures 
less  liability  from  surface  leakage  in  damp  weather,  or  on 
lines  near  the  seacoast. 

Porcelain  is  not  so  brittle  as  glass,  and  an  insulator  may 
be  chipped  or  struck  with  a  bullet  without  cracking  in  such 
a  way  as  to  cause  a  leak.  Porcelain,  however,  has  several 
disadvantages.  It  is  much  more  expensive  than  glass  ;  de- 
fects in  the  construction  of  porcelain  insulators  are  not 


THE    TRANSMISSION    LINE  2O/ 

apparent  to  the  eye,  hence  the  necessity  of  making  high- 
voltage  tests  to  determine  the  quality  and  condition  of 
the  insulators  before  they  are  put  into  use.  Such  tests  are 
quite  tedious  and  necessitate  the  use  of  expensive  apparatus. 
Furthermore,  being  rather  conspicuous  in  appearance,  por- 
celain insulators  offer  a  fine  target  to  mischievously  inclined 
riflemen  and  the  stone-throwing  small  boy.  The  shooting 
of  insulators  has  become  such  a  frequent  source  of  trouble 
to  some  Western  transmission  companies  that  statutes 
have  been  enacted  in  a  few  of  the  trans-Mississippi  States 
making  it  a  penal  offense. 

For  potentials  as  high  as  30,000  volts,  glass  can  in  most 
instances  be  more  advantageously  employed  for  insulators 
than  porcelain.  The  chief  advantage  possessed  by  glass 
over  porcelain  is  its  cheapness.  In  addition  to  this,  how- 
ever, glass  possesses  the  advantage  that  any  defects  in  it 
are  readily  visible  to  the  eye,  which  advantage  obviates  the 
expense  of  testing  each  insulator  before  it  is  mounted  on 
the  cross-arm.  The  transparency  of  glass  confers  another 
practical  advantage  over  porcelain,  in  that  it  does  not  invite 
insects  to  build  nests  within  the  insulators.  Such  nests 
are  very  liable  to  form  short  circuits  ultimately. 

The  most  important  objections  urged  against  glass  are 
its  lack  of  mechanical  strength  (it  averages  about  half  the 
strength  of  porcelain  of  the  best  grade),  and  its  hygro- 
scopic character  and  consequent  tendency  to  promote 
current  leakage  through  the  accumulation  of  moisture. 
As  an  offset  to  this  latter  fault,  however,  it  is  the  con- 
sensus of  opinion  among  both  glass  and  porcelain  advo- 
cates that  the  static  action  of  the  current  tends  to  dry 
out  any  moisture  which  may  collect  on  either  kind  of 
insulator. 


208     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

In  general,  glass  insulators  are  better  adapted  for  light 
lines  (aluminum),  and  under  conditions  which  do  not  re- 
quire insulators  larger  than  six  or  seven  inches  in  diameter. 
The  facUJthat  they  are  giving  satisfaction  on  circuits  oper- 
ating at  five  kilovolts  is  sufficient  indication  that  it  is  by  no 
means  a  settled  question  which  kind  of  insulator  is  supe- 
rior, everything  considered. 

Combination  glass  and  porcelain  and  compound  insula- 
tors are  now  in  quite  extensive  use  on  high-tension  circuits. 
Combination  insulators  are  built  up  by  cementing  an  inner 
glass  sheath,  which  contains  the  pinhole,  to  a  porcelain 
body.  In  a  compound  insulator  constructed  entirely  of 
porcelain,  the  upper  part  or  body  is  solid,  while  the  porce- 
lain base  is  cemented  in.  Combination  insulators  have 
also  been  constructed  by  cementing  three  layers  of  mate- 
rial together,  two  of  which  are  porcelain  and  the  other  of 
glass,  or  vice  versa. 

Compound  and  combination  insulators  are  much  easier 
and  cheaper  to  construct  than  solid  insulators,  but  the  die- 
lectric thus  obtained  lacks  homogeneity,  and  cannot  give 
the  insulating  properties  of  a  one-piece  dielectric. 

In  combination  insulators  the  current  stress  is  trans- 
mitted from  porcelain  to  glass,  or  vice  versa,  so  that  a  con- 
centration of  the  stress  occurs  where  the  two  surfaces  meet, 
and  these  being  the  weakest  points  in  the  insulator,  a  break- 
down is  liable  to  occur  there. 

Compound  and  combination  insulators  also  lack  mechani- 
cal strength,  since  the  contraction  of  the  plastic  material 
used  to  hold  the  layers  together  leaves  cracks  and  gives 
rise  to  unequal  strains. 

Testing  of  Insulators.  —  Insulators  of  all  kinds  should  be 
free  from  cracks,  bubbles,  and  pits. 


THE   TRANSMISSION    LINE  2O9 

The  glaze  of  porcelain  should  entirely  cover  the  outer 
surface.  Glaze  really  possesses  no  insulating  value ;  its 
purpose  is  to  prevent  the  adherence  of  dirt.  Highest 
grade  porcelain  exhibits  a  polished  or  vitreous  fracture. 

When  the  insulators  are  of  glass,  testing  js./usually 
limited  to  a  visual  examination,  followed  by  a  few  blows 
from  a  hammer  to  determine  the  soundness  of  the 
insulator. 

When  porcelain  insulators  are  used,  lengthy  and  not 
infrequently  expensive  tests  must  be  conducted  to  ascertain 
whether  the  material  is  thoroughly  vitrified,  of  homoge- 
neous character,  absolutely  impervious  to  moisture,  and 
capable  of  standing  the  voltage  stress  without  the  surface 
glaze.  Final  high-potential  tests,  usually  equal  to  double 
the  line  voltage,  must  also  be  made. 

A  low  grade  of  porcelain  is  readily  manifest  from  the 
character  of  the  fracture.  The  degree  of  porosity  is  most 
readily  determined  by  soaking  the  insulators  in  red  ink. 
After  being  washed,  thoroughly  vitrified  porcelain  shows 
no  traces  of  the  ink,  whereas  in  the  low-grade  variety  the 
ink  is  readily  absorbed  and  cannot  be  washed  out.  Unless 
perfectly  non-absorbent,  porcelain  insulators  are  of  no  value 
for  high-tension  service. 

High-potential  tests  to  determine  the  degree  of  the 
dielectric  properties  of  insulators  are  usually  made  by  put- 
ting a  number  of  the  insulators,  inverted,  in  a  metallic 
trough,  which  is  then  filled  to  a  depth  of  two  or  more 
inches  with  brine.  The  saline  solution  should  also  fill  the 
pinholes  of  the  insulators. 

A  metallic  rod  is  set  in  each  pinhole,  and  all  the  rods 
are  connected  in  series  to  one  terminal  of  a  high-tension 
transformer  or  group  of  transformers,  and  the  metallic  pan 


2IO     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


to  the  other  terminal.  The  capacity  of  the  high-tension 
supply  source  should  be  adequate  to  furnish  an  appreciable 
current  at  a  potential  approximately  double  that  of  the 
potential  which  the  insulators  will  normally  have  to  with- 
stand in  practice.  Each  part  of  a  compound  insulator 
should  be  capable  of  withstanding  a  pressure  considerably 
greater  than  it  will  be  called  upon  to  withstand  when  the 
entire  insulator  is  tested.  On  closing  the  circuit,  all 

weak  and  badly  con- 
structed insulators 
will  be  punctured 
and  a  shower  of 
intensely  luminous 
sparks  will  ensue. 

Wet  arcing  tests 
should  be  carried 
out  in  a  manner 
which  will  give  ap- 
proximately such 
conditions  as  exist  in 
rain  storms.  Such 
tests  can  be  carried 
out  by  directing  a 

stream  of  water  on  the  insulator,  under  50  or  60  pounds 
pressure,  and  at  an  angle  of  from  25  to  35  degrees  from 
the  horizontal. 

Types  of  American  Insulators.  —  Fig.  95  shows  a  Locke 
high-tension  insulator.  It  is  of  the  triple-petticoat  type 
and  is  constructed  entirely  of  brown  porcelain.  The  diam- 
eter is  1 1  inches  and  the  height  ioj  inches.  The  pinhole 
is  of  the  ij  inch  standard,  and  the  side  and  top  grooves 
are  both  I  inch. 


Fig.  95.     A  High-Tension  Porcelain  Insulator 


THE   TRANSMISSION    LINE 


211 


Fig.  96  shows  the  Locke  "  Victor "  type  of  porcelain 
insulator,  which  is 
used  on  the  trans- 
mission lines  of  the 
Bay  Counties  Power 
Compahy,  the 
Standard  Electric 
Company,  of  Cali- 
fornia, and  other 
high-tension  cir- 
cuits. It  is  of  the 
triple-petticoat  type 
and  is  14  inches  in 

diameter    and      \2\          Fig.  06.    Locke  "Victor  "Type  High-Potential 

inches     in      height.  insulator 

The  groove  at  the  top  in  which  the  conductor  is  carried 

is  }  inch  wide.     The  insulator  is  designed  for  60,000  and 

80,000  volts. 

Fig.  97  illustrates 
the  "  Provo  "  type 
of  glass  insulator 
made  by  the  Hem- 
ingray  Glass  Com- 
pany. This  is  the 
first  type  of  glass  in- 
sulator successfully 
used  on  a  40,000 
volt  circuit,  and  was 
first  applied  on  the 
105  mile  line  of  the 

Fig.  97.     A  Type  of  High-Tension  Glass  Insulator  J 

Telluride  Transmis- 
sion Company,  of  Colorado.     It  is  of  the  triple-petticoat 


5^  High 
IT  "Diameter 


212     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


type  and  is  7  inches  in  diameter  and  5J  inches  in 
height. 

Fig.  98  shows  the  "Muncie"  type  of  Hemingray  glass  in- 
sulator with  sleeve,  and  Fig.  99  is  a  sectional  sketch  of  the 
same  insulator  with  all  dimensions  appended,  as  applied  to 
the  57,000  volt  circuit  of  the  Missouri  River  Power  Com- 
pany.  This  type  of  in- 
sulator was  designed 
by  Mr.  M.  H.  Gerry, 
Jr.,  chief  engineer  of 
the  Missouri  River 
Company. 

Devices  for  Fas- 
tening Conductors 
to  Insulators.  —  Fig. 
100  shows  a  Clark 
insulator  clamp  de- 
signed for  use  with 
standard  insulators. 
It  comprises  two 
clamps  which  are  rig- 
idly secured  to  the 
conductor  on  either 

Fig.  98.     Type  of  Glass  Insulator  Used  on  a  57,ooo      sj^e    Q£    j-Qe    insulator 
Volt  Circuit 

by  means   of   a  bolt 

and  nut.  The  projecting  ends  engage  the  groove  of  the 
insulator  and  thus  transfer  the  end  strain  to  the  insulator. 
The  loop  encircling  the  neck  of  the  insulator  holds  the 
clamps  firmly  in  position  and  prevents  the  conductor  from 
being  lifted  from  the  groove.  Fig.  101  shows  the  Clark 
interlocking  insulator  clamp  for  holding  the  cable  or  con- 
ductor in  the  groove  of  the  insulator.  Insulators  designed 


THE   TRANSMISSION    LINE 


213 


for  the  use  of  this  type  of  clamp  are  made  with  an  under- 
cut recess  on  either  side  of 
the  groove  in  the  center  of 
the  insulator  top,  so  that 
when  the  clamp  is  in  position 
it  is  interlocked  under  the 
projecting  portion  in  such  a 
manner  that  the  conductor 
cannot  be  removed  or  the 
clamp  separated  from  the 
insulator  without  unlocking 
the  clamp.  This  type  of 
clamp  is  made  in  sizes 
ranging  from  No.  2  bare  to 
500,000  circular  mils 
weather-proof  wire.  Fig. 
1 02  shows  the  position  of 
the  clamp  in  the  insulator. 
The  underlocking  insulator 
clamp  (Fig.  103)  is  employed 
on  transmission  lines  with 
long  spans  or  such  lines  as 

Fig.  99  .       Sectional  View  of  Insulator 

are    subject    to    the    strains  shown  in  Fig.  98 

occasioned  by  high  winds  or  sleet.      In  this  type  of  clamp 

the  conductor  is 
fastened  on  each 
side  of  the  insu- 
lator. The  pro- 
jections or  lips 
engage  a  deep 

Fig.  zoo.     Clamp  for  Use  on  Standard  Insulators 

annular     groove 
in  the  neck  of  the  insulator  which  prevents  the  wire  from 


214    LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 


being  torn  from  the  groove,  and  transfers  the  end  strain 

over   a  wide  area  of  conductor.     Two  such   clamps   are 

required  for  each  insulator. 

Methods  of  Stringing  Wires.  — 
Three  methods  of  stringing  wires 
are  employed  by  American  long- 
distance transmission  companies, 
-  parallel,  in  an  isosceles  triangle, 
and  in  an  equilateral  triangle.  In 
parallel  work  the  several  conduc- 
tors of  the  circuit  are  supported 
on  the  same  cross-arm.  This  is 

the  method  usually  adopted  when  two  or  more  circuits  are 

carried  on  a  pole  line. 


Fig.  101.    An  Interlocking 
Insulator  Clamp 


Fig.  102.    Interlocking  Clamp  in  Position 

When  wires  are  strung  at  the  corners  of  an   isosceles 
triangle    two  cross-arms  per  pole  are  used.     This  is  the 


THE   TRANSMISSION    LINE 


215 


general  method  adopted  when  two  separate 'transmission 
lines  are  carried  on  one  pole  line.  In  this  method  of 
stringing  wires  the  interaxial  distance  between  the  upper 
conductor  and  each  of  the  two  lower  ones  (assuming  a 
three-wire  circuit)  is  different  from  that  between  the  two 
lower  wires. 

This  method  necessitates  frequent  spiraling  and  trans- 
positions of  the  two  circuits,  in  order  to  overcome  unequal 
effects  of  inductance  in  the  different  legs,  as  well  as  to  neu- 
tralize the  mutual  induction  and  capacity  between  the  two 
lines.  Means  must  also  be  adopted  to  balance  the  capacity 
of  the  separate  legs  of  both 
circuits  with  respect  to 
each  other.  Fig.  104  shows 
the  usual  method  of  string- 
ing two  circuits  on  the 
same  pole  line. 

In  three-phase  transmis- 
sions with  common  return, 

which   is  now    generally  ac-  Fig.  103.   An  Underlocking  Insulator 

cepted  as  the  most  efficient  Clamp 

and  economical  method  of  transmitting  energy  over  long 
distances,  the  three  conductors  of  a  circuit  are  placed  at 
points  of  an  equilateral  triangle  and  separated  from  each 
other  by  distances  varying  in  practice  from  18  to  78 
inches.  Fig.  105  shows  a  typical  method  of  stringing 
conductors  in  the  form  of  an  equilateral  triangle.  The 
circuit  in  question  is  that  of  the  Missouri  River  Power 
Company. 

Transposition  of  Wires.  —  When  two  circuits  are  strung 
on  one  pole  line,  transpositions  of  conductors  become  es- 
pecially important  and  somewhat  complex,  since,  as  pre- 


2l6     LONG    DISTANCE    ELECTRIC    POWER   TRANSMISSION 

viously  stated,  it  then  becomes  necessary  to  neutralize  the 
effect  of  unequal  inductance  in  the  different  legs  of  the 


Fig.  104.    Usual  Method  of  Stringing  Two  Circuits  on  Same  Pole  Line 

circuit  (if   their   interaxial   distances  vary),  and  overcome 
mutual  induction  between  the  two  lines. 

The  number  of  transpositions  required  on  long-distance 
lines  vary  with  the  working  conditions,  such  as  the  distance 


THE   TRANSMISSION    LINE 


217 


apart  of  the  different  legs  of  the  circuit,  the  number  of 
wires  on  a  pole  line,  the  transmission  voltage,  and  the  prox- 
imity of  telephone  or  telegraph  wires.  In  American  prac- 


POLETOP 

Pig.  105.  Equilateral  Triangle  Arrangement  of  Conductors  Used  on  57,000  Volt 
Line  of  Missouri  River  Power  Company 

tice  transpositions  are  made  at  distances  varying  from  one 
mile  up  to  fifteen  miles. 

In  the  equilateral  triangle  lay-out  of  wires  used  on  three- 
phase  circuits,  the  transposition  of  conductors  is  not  con- 


2l8      LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

sidered  absolutely  necessary,  unless  it  is  impractical  to  carry 
the  telephone  circuit  at  a  distance  of,  approximately,  eight 
feet  below  the  power  line.  With  steel-supporting  struc- 
tures for  carrying  lines  transpositions  may  be  entirely  dis- 
pensed with. 

When  telephone  wires  are  carried  on  the  same  pole  line 
with  the  power  wires,  and  in  close  proximity  thereto,  as  is 
frequently  the  case  on  long-distance  circuits,  special  pre- 
cautions should  be  taken  to  prevent  inductance  troubles. 

As  telephone  communication  is  absolutely  necessary  be- 
tween the  generating  and  receiving  stations  of  long-dis- 
tance lines,  and  as  economical  considerations  usually  require 
that  the  telephone  circuit  be  strung  on  the  same  pole  line 
with  the  power  circuit,  the  proper  transposition  of  power 
and  telephone  wires  is  of  the  highest  importance  in  order 
to  prevent  serious  disturbances  due  to  both  electromagnetic 
and  electrostatic  effects. 

Proper  transposition  of  the  telephone  wires  when  they 
are  carried  on  the  same  pole  line  with  power  wires  is  more 
important  than  the  transposition  of  the  power  wires  them- 
selves ;  for  if  the  telephone  wires  be  properly  transposed, 
the  untransposed  power  circuit  cannot  set  up  electromag- 
netic and  electrostatic  disturbances  in  the  telephone  wires, 
but  will  produce  such  effects  only  between  themselves  and 
the  ground. 

Considerable  care  must  be  observed  in  making  transposi- 
tions to  avoid  side  strains  on  the  line.  Fig.  106  shows  the 
usual  method  of  transposing  two  three-phase  circuits. 

Length  of  Spans.  —  The  length  of  span  which  should 
be  used  on  high-tension  circuits  varies  with  the  operating 
conditions  and  the  factor  of  safety  desired.  No  specific 
rules  are  applicable. 


THE   TRANSMISSION    LINE 


2I9 


Fig.  106.     Transposition  of  Two  Three-Phase  Circuits 


220     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

The  length  of  span  used  on  copper  transmission  lines 
varies  from  90  to  150  feet.  Standard  practice  is  now 
tending  towards  the  use  of  106  foot  spans  on  copper  lines 
carried  on  wooden  poles,  which  makes  about  fifty  poles 
per  mile. 

On  aluminum  lines  the  spans  are  frequently  as  long  as 
176  to  212  feet,  requiring  from  25  to  30  poles  per  mile. 
Much  difference  of  opinion  exists  as  to  the  advisability 
of  lengthening  the  span  of  aluminum  lines  on  account  of 
the  appreciable  lightening  of  the  weight  on  cross-arms  and 
insulators  secured  by  the  use  of  aluminum.  In  most 
cases  the  advantage  of  lightness  thus  obtained  should  not 
be  utilized  in  decreasing  the  line  expense,  but  should  be 
applied  to  increase  the  factor  of  safety,  and  the  same 
length  of  span  should  be  used  for  both  kinds  of  con- 
ductors. 

Protection  of  Transmission  Lines  from  Lightning.  — 
Many  of  the  troubles  to  which  high-tension  lines  are  sub- 
ject are  due  to  the  effects  of  lightning.  The  extent  to 
which  long-distance  circuits  suffer  from  lightning  dis- 
turbances varies  with  the  climatic  conditions  of  the  region 
which  a  line  traverses,  being  much  more  severe  in  semi- 
tropical,  tropical,  and  mountainous  regions  than  in  northerly 
countries. 

The  problem  of  effectively  protecting  high-potential 
lines  from  the  destructive  effects  of  lightning  is  one  that 
has  not  as  yet  been  completely  solved.  In  fact,  the 
capricious  action  of  lightning  often  entirely  sets  at  naught 
the  safeguards  provided  to  protect  the  lines. 

Lightning  generally  affects  an  aerial  line  in  three 
different  ways,  —  by  direct  stroke,  by  induced  charges, 
and  by  electrostatic  induction. 


THE   TRANSMISSION    LINE  221 

Disturbances  due  to  direct  strokes  of  lightning  are  of 
rare  occurrence.  In  such  cases  no  arrester  in  existence 
can  completely  neutralize  the  effects  of  it  on  the  line. 

Induced  discharges  caused  by  the  electromagnetic  effect 
of  a  lightning  flash  are  a  frequent  source  of  trouble. 

Electrostatic  charges  giving  rise  to  electrostatic  induc- 
tion are  due  to  charges  in  the  surrounding  atmosphere. 

Since  a  lightning  discharge  is  of  enormously  high  fre- 
quency, inductance  in  the  line  opposes  a  very  high  im- 
pedance to  a  discharge,  and  the  discharge  takes  the 
shortest  and  most  direct  passage  to  ground.  This  ac- 
counts in  a  large  measure  for  the  puncturing  of  transformer 
coils. 

Since  inductance  in  the  line  offers  great  resistance  to 
the  passage  of  a  lightning  discharge  this  fact  is  sometimes 
taken  advantage  of  by  putting  choke  coils  in  series  with  the 
line,  and  between  the  arrester  and  the  central  station. 
Such  choke  coils  are  made  of  flat  copper  strip,  wound  on  a 
non-conducting  core,  the  separate  layers  being  insulated 
with  mica. 

This  combination  described  works  fairly  satisfactory  as 
a  protecting  device  for  the  station  apparatus,  but  its  cost 
makes  its  use  prohibitive  on  every  line  arrester  unless  it 
is  imperative  to  give  the  utmost  possible  protection  to  the 
apparatus. 

Practice  differs  as  regards  the  use  of  arresters  at  various 
points  along  high-tension  lines.  Some  transmission  com- 
panies use  arresters  only  in  the  generating  station  and  at 
sub-stations.  To  safeguard  a  circuit  effectively,  arresters 
should  be  located  at  the  ends  of  all  lines,  at  sub-stations,  and 
at  points  where  the  lines  branch  off. 

Many  transmission  companies  rely  partly  or  wholly  upon 


222    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

a  grounded  wire  along  the  lines  as  a  safeguard  against  dam- 
age by  lightning.  Such  wires  are  made  of  either  smooth 
galvanized  iron  in  the  solid  or  cable  form,  or  in  the  shape 
of  barbed  wire,  and  strung  parallel  to  the  power  wires  and 
grounded  at  intervals.  Such  a  grounded  wire  constitutes  a 
short-circuited  secondary,  which  largely  absorbs  by  induc- 
tion the  energy  of  a  lightning  discharge  to  the  line.  A 
grounded  wire  strung  near  power  wires  also  serves  to  dis- 
charge any  charged  atmosphere  which  may  blow  across  the 
line. 

Another  advantage  is  afforded  by  a  grounded  parallel 
wire  in  cases  where  transmission  lines  run  through  moun- 
tainous regions,  in  which  there  are  marked  differences  in 
the  altitude  of  different  parts  of  the  line.  Under  such  con- 
ditions there  is  an  electrostatic  effect  due  to  differences  in 
altitude,  which  produces  an  appreciably  greater  difference 
of  potential  between  conductors  and  the  ground  in  the  low 
than  in  the  high  altitudes. 

When  parallel  grounded  wires  are  depended  upon  for 
protection,  three  such  wires  are  usually  employed,  one 
wire  being  strung  on  top  of  the  pole,  and  one  at  each 
end  of  the  cross-arm.  In  order  to  give  them  reliable 
mechanical  support  they  are  usually  mounted  on  pony 
insulators. 

Frequent  grounding  is  necessary  in  order  that  the  oppo- 
sition to  the  flow  of  current  between  the  grounded  wire 
and  the  earth  will  be  reduced  to  a  minimum. 

Surges  in  Transmission  Lines.  —  The  chief  causes  of 
surges  in  high-tension  circuits  are  opening  a  line  carrying 
a  load  or  under  a  short  circuit,  closing  a  high-potential 
line  switch  to  charge  the  line,  and  opening  a  high-tension 
switch  to  make  the  line  dead. 


THE   TRANSMISSION    LINE  223 

The  worst  cases  of  damage  to  apparatus  by  surges  are 
those  produced  by  the  sudden  rupture  of  a  short  circuit. 
This  is  due  to  the  fact  that  the  current  which  the  line  is 
carrying  at  the  time  of  the  short  circuit  is  considerably  in 
excess  of  the  maximum  normal  operating  current ;  the 
magnitude  of  alternating-current  surging  depends  upon  the 
value  of  the  current  at  the  instant  of  rupture. 

If  the  interruption  takes  place  at  the  zero  point  of  the 
current  wave,  the  surge  which  follows  is  slight  enough  to 
be  considered  negligible,  but  if  the  interruption  occurs  at 
the  peak  or  crest  of  the  current  wave  the  surging  has  a 
value  which  is  the  same  as  that  which  would  be  produced 
by  a  direct  current  of  the  same  strength. 

If  the  conditions  of  operation  render  it  possible  to  break 
the  short  circuit  gradually  through  external  resistance,  the 
surging  will  not  be  of  appreciable  importance.  The  surg- 
ing will  also  be  slight  if  the  current  wave  can  be  stopped 
by  automatic  means  at  or  very  near  its  zero  point. 

When  the  line  switch  is  first  closed  on  a  dead  line,  charg- 
ing current  at  once  flows  into  the  line,  which  is  a  simple 
condenser.  But  this  charging  current  is  obliged  to  flow 
through  the  line  inductance,  and  this  stores  up  energy  in 
the  shape  of  a  magnetic  field.  The  stored-up  energy  then 
discharges  into  the  condensive  line  and  so  adds  to  the 
charge  already  in  it.  The  maximum  possible  E.M.F.  from 
this  cause  is  double  the  working  potential  of  the  line. 

In  opening  a  line  switch  to  disconnect  a  circuit,  the 
condenser  of  the  circuit  discharges  across  the  terminals  of 
the  switch  the  instant  they  are  separated  ;  and  owing  to 
the  charging  current  of  the  condenser,  the  pressure  of  the 
circuit  rises  to  its  maximum  value  of  operation  at  the  nor- 
mal frequency  of  the  line. 


224    LONG    DISTANCE    ELECTRIC    POWER   TRANSMISSION 

Hence  before  the  switch  can  be  pulled  very  far  apart,  the 
line  pressure  set  up  by  the  oscillating  current  in  the  circuit 
is  superposed  on  the  pressure  between  the  switch  ter- 
minals due  to  the  generator.  Such  increase  of  potential 
may  cause  the  arc  to  oscillate  several  times  between  the 
switch  jaws  before  the  circuit  becomes  absolutely  dead. 

The  surge  following  the  opening  of  a  high-tension  line 
may  cause  a  rise  of  potential  equal  to  double  the  normal 
operating  pressure. 

Very  great  precautions  should  be  exercised  in  opening 
a  high-potential  circuit  under  load,  as  destructive  voltages 
are  liable  to  ensue. 

When  an  alternating  current  is  suddenly  interrupted 
at  the  receiving  end  of  a  line  its  natural  outlet  is  sup- 
pressed. It  at  once  flows  into  the  condenser  and  charges 
the  circuit,  but  since  the  condenser  cannot  hold  the  charge, 
it  discharges  into  the  self-inductance  of  the  line,  and  the 
energy  is  converted  into  magnetic  energy. 

The  magnetic  field  then  gives  up  its  energy  to  the  con- 
denser, and  the  cyclical  exchange  of  energy  is  repeated  in 
gradually  decreasing  amplitude  until  the  line  resistance 
has  consumed  the  energy  at  first  stored  in  the  line  self- 
inductance. 

The  surges  or  oscillatory  currents  set  up  in  this  way  are 
of  a  very  serious  character,  and  may  completely  destroy 
or  at  least  severely  strain  the  insulation  of  the  generating 
or  the  transforming  apparatus,  or  both. 

Losses  by  Leakage  and  Electrostatic  Induction,  — 
Aside  from  the  difficulties  of  effectively  insulating  the  line, 
the  limitations  to  the  potentials  practical  for  electric  power 
transmission  are  losses  by  line  leakage  and  electrostatic 
induction. 


THE   TRANSMISSION    LINE  22  5 

Leakage  losses  take  place  from  wire  to  wire  of  the 
circuit,  and  with  very  high  potentials  may  reach  enormous 
values,  unless  the  conductors  are  made  unduly  large  and 
are  widely  separated. 

A  very  interesting  series  of  experiments  were  carried 
out  by  Mr.  Charles  F.  Scott,  to  ascertain  the  losses  by 
leakage  on  high-tension  circuits  and  the  limitations  to  long- 
distance power  transmissions.  The  results  of  his  experi- 
ments may  be  thus  summed  up  :  The  power  loss  through 
the  air  by  current  leakage  between  wires  increases  with 
the  impressed  voltage,  and  after  a  critical  voltage  is 
reached  it  increases  very  rapidly.  With  a  given  impressed 
voltage  the  loss  decreases  as  the  distance  between  wires  is 
increased.  The  loss  is  not  appreciably  affected  by  atmos- 
pheric conditions,  such  as  rain,  snow,  or  humidity. 
Peaked  E.M.F.  wave  shapes  give  greater  losses  than  flat- 
topped  waves.  The  loss  decreases  as  the  diameter  of  the 
wires  increases. 

His  results  were  summed  up  in  a  set  of  curves,  repro- 
duced in  Fig.  107,  showing  the  relations  between  wire 
distance,  operating  voltages,  and  power  loss.  Fig.  108 
shows  the  loss  when  the  distance  between  conductors  was 
increased  to  48  inches. 

Dr.  Steinmetz  found  in  his  experiments  on  the  electric 
disruptive  strength  of  powerful  solid  dielectrics  that  the  at- 
mosphere surrounding  the  solid  dielectric  specimen  and  the 
electrodes  applied  thereto  would  rupture  under  the  strain 
produced  by  the  flux  of  electric  force  through  it  much 
easier  than  the  solid  dielectric.  This  produces  envelopes  of 
conductive  atmosphere  around  the  electrodes  and  over  the 
surface  of  the  strong  dielectric,  which  phenomenon  re- 
sembles a  brush  discharge  from  a  static  machine,  and  is 


226    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

termed  the  corona.  Corona  formation  depends  primarily 
upon  the  maximum,  and  not  upon  the  effective  value  of 
the  E.M.F.  wave,  as  has  been  shown  by  the  experiments 
of  Scott,  Mershon,  Ryan,  etc. 

The  experimental  work  of  Steinmetz  has  also  shown 
that  the  atmosphere  conducts  after  disruption  in  two  forms, 
cither  arcs  or  intensely  heated  streamers  at  high-current 


12.5 


60 


Fig.  107.    Curves  Showing  Power  Losses  at  Various  Voltages  and  Spacings 

of  Wires 

density,  or  coronal  or  brush  discharges  at  lower  current 
density.  The  latter  begin  to  appear  at  pressures  above 
40,000  volts.  Steinmetz  further  ascertained  that  the 
dielectric  strength  of  the  atmosphere  in  bulk  requires 
approximately  a  potential  gradient  of  10,000  effective 
volts  per  inch,  with  an  E.M.F.  wave  following  the  sine 
law, 


THE   TRANSMISSION    LINE 


227 


The  researches  of  Professor  Ryan  (Trans.  A.  I.  E.  E. 
Vol.  21)  show  that  the  critical  voltage  of  a  brush  or 
coronal  discharge  is  a  function  of  the  barometric  pressure 
of  the  air  :  his  equation  for  this  is 

Kv  —  0.902  b  4-  2.93, 

where  Kv  —  effective  kilovolts  and  b  =  barometric  pressure  in 
inches  of  mercury. 


20  30  40  50  60 

KILOVOLTS 

Fig.  108.    Curves  Showing  Losses  with  Wires  48  Inches  Apart 


Hence  on  lines  crossing  high  altitudes  the  pres- 
sures which  are  permissible  are  appreciably  less  than 
those  which  the  same  line  construction  admits  of  at  sea 
level. 

Danger  of  brush  discharge  becomes  less  as  the  size  of 
the  conductor  increases.  A  large  conductor  therefore 
permits  the  use  of  higher  voltages  than  a  small  one,  and 


228     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

aluminum  conductors   diminish   the   tendency    of   coronal 
discharges. 

The  equation,  according  to  Professor  Ryan,  which  gives 
the  maximum  voltage  causing  corona  formation,  is, 

£max  —  —       — ~.  *  2055  (r+d)  Iog10  f-J  D'  x  io10 

where  Emax  =  maximum  value'  of  the  potential  wave  impressed 
upon  the  line. 

b  =  barometric  pressure  in  inches  of  mercury. 

/  =  temperature  in  degrees  Fahr. 

s  =  separation  of  line  conductors  from  center  to  center, 
in  inches. 

d  =  distance  from  conductor  surfaces  at  which  the 
strain  due  to  the  electrostatic  field  causes 
rupture  of  the  atmosphere. 

P'  =  the  dielectric  flux  density,  in  coulombs  per  square 
inch,  that  will  electrically  rupture  the  atmos- 
phere at  distance  d  from  the  surface  of  the 
conductor  having  a  radius  r. 

"For  wires  of  0.25  inch  in  diameter  and  upwards,  Df 
and  d  remain  constant  at 

Df  =  170  x  io~10  coulombs  per  square  inch  and 
d  =  0.07  inches." 

Hence  for  such  wires  Ryan's  equation  becomes, 

Emax = d7Q9+ 1 x  35°'oo°  ( r + °-°7)  iogi°  0  • 

i  3  V    ^  \    / 

Grounding  of  High-Potential  Lines.  —  Grounding  the 
neutral  point  of  a  high-tension  line  is  desirable  for  the  fol- 
lowing reasons  :  When  the  neutral  point  is  grounded  the 
voltage  between  the  conductors  and  the  ground  is  limited 
to  the  operating  potential  of  the  line.  In  an  ungrounded 
line,  the  voltage  between  phase  conductors  and  ground 


THE    TRANSMISSION    LINE  229 

may  vary  between  wide  limits,  and  may  attain  such  values 
that  the  liability  to  the  breakdown  of  the  line  insulation 
becomes  serious.  When  a  high-potential  line  is  grounded, 
it  insures  the  immediate  detection  of  faults  and  necessi- 
tates their  immediate  removal. 

One  objection  to  grounding  is  that  it  increases  the  ele- 
ment of  danger  to  persons  and  property.  It  is  the  general 
opinion  that  the  fact  of  the  conductor  voltages  being  main- 
tained at  a  definite-arid  dangerous  value  above  the  ground 
potential  is  sufficient  proof  that'  the  danger  to  life  is  greatly 
augmented  by  the  practice. 

As  an  illustration :  If  the  neutral  is  grounded,  the  oper- 
ating Y-pressure  of  the  system  is  introduced  between  any 
line  wire  and  the  ground,  and  on  making  a  contact  to 
ground,  a  body  touching  this  contact  would  be  subject  to 
this  pressure. 

Hence  if  capacity  were  not  present,  grounding  the  neu- 
tral point  would  augment  the  element  of  danger  ;  but  since 
capacity  is  always  present  to  a  greater  or  less  degree, 
each  wire  is  really  grounded  through  a  condenser.  And 
although  the  conditions  are  slightly  different  from  the  case 
of  one  conductor  grounded  direct,  the  results  are  nearly 
alike. 

Thus  the  action  of  these  capacity  connections  to  ground 
will  be  to  cause  the  E.M.F.'s  to  concentrate  themselves 
about  the  point  of  earth  potential. 

And  so  when  the  line  wires  have  a  capacity  effect,  there 
are  differences  of  potentials  between  them  and  the  ground, 
even  with  no  part  of  the  system  grounded  direct.  Such 
differences  of  potential  will  not  be  neutralized  by  connect- 
ing the  conductor  to  ground  through  resistance,  since  the 
capacity  behaves  like  an  elastic  band,  and  tends  to  check 


230     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

the  displacement  of  the  conductor  E.M.F.'s  relative  to  the 
earth. 

However,  the  difference  of  potential  will  be  diminished 
by  the  flow  of  current  through  the  resistance,  and  when 
the  current  is  of  considerable  strength,  may  be  reduced  to 
a  non-dangerous  value. 

The  effect  in  any  particular  case  will  depend  upon  the 
value  of  the  capacity  in  the  several  wires,  and  also  upon 
the  resistance  of  the  grounding  substance. 

Maintenance  of  Pole  Lines.  —  Patrolling  of  high-tension 
lines  becomes  essential  in  direct  proportion  to  the  potential 
employed  for  transmission,  and  the  difficulties  of  operation. 
Current  practice  as  regards  the  patrolling  of  lines  differs 
quite  widely.  Some  companies  have  ,  their  lines  patrolled 
daily,  some  weekly,  while  others  do  so  only  at  intervals  of 
one  or  several  months.  The  character  of  the  country 
which  the  line  traverses  is  an  important  factor  in  deter- 
mining the  frequency  for  making  inspections. 

The  necessity  for  patrol  trips  is  considerably  obviated 
by  the  use  of  telephone  lines  on  the  same  poles  with  the 
transmission  circuits.  When  a  short  circuit  or  a  dangerous 
leakage  has  occurred  on  the  power  circuit,  the  peculiar 
sounds  given  out  by  the  telephone  receiver  render  the  fact 
of  its  occurrence  unmistakable. 

On  circuits  where  patrolling  is  carried  out  the  line  is 
divided  into  sections  varying  from  10  to  20  miles  in 
length,  each  of  which  is  assigned  to  a  patrolman.  In 
order  to  enable  the  patrolman  to  make  reports  to  the  cen- 
tral station,  taps  are  brought  down  from  the  telephone 
circuits  to  booths  located  a  few  miles  apart,  to  which  the 
patrolman  makes  connection  with  his  portable  telephone 
set  and  informs  the  station  attendants  of  the  condition  of 


THE   TRANSMISSION   LINE 

the  line.  As  a  precaution  against  the  danger  of  a  high- 
voltage  discharge  through  the  telephone  line,  each  booth 
is  provided  with  a  highly  insulated  stool  upon  which 
the  trouble  man  sits  in  calling  up  the  central  or  sub- 
station. 

Calculation    of    a  75    Mile    Three-Phase    Transmission 
Line.  — 

Data  :  2,000  k.  w.  with  line  loss  of  3  per  cent. 

25  ~w  Frequency. 

.85  Power  Factor. 

Copper  Conductors. 

Assume  30,000  volts  as  the  pressure  of  transmission  and 
consider  one  leg  of  the  circuit. 

Then       *  _  —  =  17320  volts  =  E.M.F.  between  any  wire  and 

V3 

the  neutral  point. 


icooo  X  2 
A=  --  •=--  =  17320 

V3 

The  energy  delivered  by  each  leg  is 

2060    k.w. 

-  =  686.6  k.w. 

3      ^ 
The  apparent  energy  delivered  by  each  leg  is 

686.6   k.w. 

—  =  808,000  watts 
•85 

The  current  in  each  leg  is 

808000 

—  -  =46.6  amperes. 
17320 


232    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

To  determine  the  size  of  conductor  necessary,  assume  the 
limit  of  the  IR  drop  to  be  10  per  cent  of  the  voltage  in 
each  leg : 

10  per  cent  of  17320  =  1732  volts. 

Hence, 

J?  =  l^  =  37.2  ohms. 
46.6 

And  the  ohms  per  1,000  feet  are, 

=  0.965  ohms  per  1000  ft. 


S-2^  X  75 
.    (5.28  is  the  ohms  per  mile  of  wire.) 

Therefore,  we  use  No.  oo  wire  whose  radius  R  is  0.78 
per  1,000  feet  by  table. 

And  the  total  resistance  of  one  leg  is 

0.78  X  75  X  5.28  =  30.9  ohms. 

The  inductance  of  one  leg  per  mile  is 

r  /^\-|io-« 

L  (in  henrys)  =    80.5  +  740  log  f  -  1 

d=  18  inches  =  45.8  cms. 
R  =  ^—5  2.54  =  ^462  cms. 


=  (80.5  +  740  log  99.3)  10-« 

=  (80.5  +  740    X    1.996949)  W 

=  80.5  +  1470  =  1550.5  = 

1  ,000,000          1  ,000,000 


in  henrys  per  wire  per  mile. 


THE   TRANSMISSION    LINE  233 

The  total  inductance  of  each  leg  is 

.00155  x  75  =  -IJ7  henry's. 
The  inductance  in  ohms  is 

2  TT/Z  =  2  x  3.14  X  25  x  .117  =  18.4  ohms. 

The  capacity  of  the  line  in  microfarads  is 


2  lo§io  - 

where 

L  =  length  of  line  in  miles. 

d  =  distance  between  wires  in  inches. 

r  =  radius  of  wire  in  inches. 


5.8*  5-8* 

2  X 


=  ~  —  =  1.46  microfarads. 
3-99° 

C  in  farads  =  1.46  X  10  6  =  .00000146. 

The  charging  current  per  wire  per  leg  is 

_  E  x  C  x  27r  x/ 
•*«  —  ~        /— 

V3  X  io6 

where 

E  =  E.M.F.  between  wires. 
/=  frequency. 
C  =  capacity  in  microfarads  between  one  wire 

and  the  neutral  point. 
Hence 

__  17,320  x  1.46  x  2  x  3.14  x  25  _ 

°  —  i~ 

V3  X  1,000,000 

.405  amperes  per  wire  per  line. 


234    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

The    E.M.F.   required   to  force  this   charging  current 
through  each  leg  is 


.-.  Ec  = =  4*  co  volts. 

2  X  3.14  X  25  X  .00000146 

The  charging  current  drop  is  1,760  volts. 
And  the  drop  due  to  charging  current  plus  the  load  cur- 
rent is 

JSe+t  =  46.3  X  30.9  =  1430  volts  drop. 

The  drop  due  to  inductance  is 

EL  —  2  TrfLI=  18.4  X  46.3  =  852  volts. 

Explanation  :  E  and  /  differ  in  phase  by  31°,  while  Ic 
and  Ec  are  90°  ahead  of  E.  Taking  the  resultant  of  /and 
7C,  one  gets  7c  +  t-,  in  phase  with  Ec. 

Finding,  by  trigonometry,  the  angle  between  this  Ec  and 
Et  multiplying  this  by  the  cosine  and  combining  the  result 
-with  EL. 

90°  ahead  of  this  Ec  is  E.  Finding  the  angle  between 
E  and  EL  we  take  its  cosine  and  resolve  EL  on  E. 

The  result  is  the  total  E. 

179°  —  60' 
121    -45 


Cos  A  = 


58°    -i5'  =  C 
<?  —  #2  _  2171  +  2170  —  .164 


2  be  2  X  46.6  X  46.3 

=  4300X488 
43i5  X  16 

A  =  4°  45' 

B  =  <£  -  A  =  31°  45'  -  4°  45'  =  27° 

D  =  90°  -  B  =  63° 


THE   TRANSMISSION    LINE  235 

and 


_ 

7C  +  Z  =  C=   \la>  +  P  -  2  ab  cos  C 

C=^°  15' 
a  =  .405 
b  =  46.6 

Then  _ 

/c+z  =   V.  1  6402  5  +  2171.56  -  3778  X  .5262 
2171.56  —  19.8 


=  46.3  amperes  for  /capacity  +  load  current. 
Cos  63°  =  CosZ>  =  .4540 
Cos  27°  =  Cos^  =  .8910 

Fig.  109  is  a  vector  diagram  showing  the  magnitude  of 
the  various  quantities  in  the  above  calculation. 

Combining  the  volts  vectorially  one  gets  (Fig.  1  10) 
EL  X  Cos  63°  =  852  X  .4540  =  386-8 

^capacity  +  load    X    COS   27°   =    1430    X     .89  I    =    1274.! 

^totai  =  I7320  +  1274.1  H-  386.8  =  18981 
y;otal  =  46.3  amperes. 

The  above  calculations  are  for  one  leg  of  the  circuit,  and 
the  voltage  is  considered  between  one  wire  and  the  neutral 
point. 

Multiplying  this  voltage  (18,981)  by  the  %/3  we  obtain 
32,820  as  the  total  line  voltage. 

The  true  power  factor  is 

Cos  27°  =  .891. 

The  regulation  of  the  line  is 

32820  -5-  30000  =  9.4  per  cent. 
Then  kilowatts  at  generator  = 

32820  x  46.3  X  89.1  x  3 

—  -=?-       —  =  2350  +  3  per  cent 
1000  X  V3 

=  2450  kilowatts  at  89.1  per  cent  power  factor. 


236    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


Using  a   I   to  6  step-up  transformer  the  E.M.F.  of  the 
generator  will  be  5,500  volts. 

X  1000 


A      i  ^i  ^ 

And  the  current, 


=  445  amperes. 


OR  SOLVING  VECTORIALLY  ONE  GETS 
I, 


Fig.  109 

Generator  specifications  : 
3 -phase  alternator  of  re- 
volving field  type. 
2,450  k.w.  or  3,290  h.p. 
5,500  volts. 


I  CAPACITY+LOAD 

Fig.  no 


445  amperes 
25  cycles. 
94  r.p.m. 
32  poles. 


To  be  direct  connected  to  an  impulse  water-wheel  of  3,560 
h.p.  output,  which  allows  for  92^  generator  efficiency. 


THE   TRANSMISSION    LINE  237 


BIBLIOGRAPHY 

Electrical  Conductors.  —  Perrine.  D,  Van  Nostrand  Co.  New  York. 
1902. 

Data  Relating  to  Electrical  Conductors  and  Cables.  —  Fisher.  Pro- 
ceedings American  Institute  Electrical  Engineers,  Vol.  24,  p.  687. 

The  Use  of  Aluminum  Line  Wire  and  Some  Constants  for  Transmis- 
sion Lines.  —  Perrine  and  Baum.  Transactions  American  Institute  Elec- 
trical Engineers,  Vol.  18,  p.  391. 

Mechanical  Specifications  for  a  Proposed  Insulator  Pin.  —  Mershon. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  20. 

Burning  of  Wooden  Pins  on  High-Tension  Transmission  Lines.  — 
Chesney.  Transactions  American  Institute  Electrical  Engineers,  Vol.  20, 
P-  435- 

Testing  of  Insulators.  —  Blackwell.  Transactions  American  Institute 
Electrical  Engineers,  Vol.  20. 

Overhead  High-Tension  Distributing  Systems  in  Suburban  Districts.— 
Lukes.  Transactions  American  Institute  Electrical  Engineers,  Vol.  21, 
P-25. 

Methods  of  Bringing  High-Tension  Wires  into  Buildings.  —  Skinner. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  20,  p.  1171. 

Transposition  and  Relative  Location  of  Power  and  Telephone  Wires. 
—  Lincoln.  Transactions  American  Institute  Electrical  Engineers,  Vol.  20. 

The  Protection  of  Telephone  or  Telegraph  Wires  When  in  Hazardous 
Proximity  to  High-Tension  Lines.  —  Chetwood.  Electrical  World  and 
Engineer,  New  York,  May  21,  1904,  p.  968. 

The  Prevention  of  Crosses  between  Signalling  and  High- Voltage  Cir- 
cuits. —  Knowlton.  Electrical  World  and  Engineer,  New  York,  April  23, 
1904,  p  768. 

The  Grounded  Wire  as  a  Protection  against  Lightning.  —  Mershon. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  20,  p.  1180. 

Grounding  of  High-Potential  Systems.  —  Nies.  Electrical  World  and 
Engineer,  April  12,  1902,  p.  639. 

Theoretical  Investigations  of  Some  Oscillations  of  Extremely  High 
Potential  in  Alternating  High-Potential  Transmissions.  —  Steinmetz. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  18,  p.  383. 

The  Regulation  of  Transmission  Lines. — Lighthipe.  Transactions 
Pacific  Coast  Transmission  Association,  San  Francisco,  July,  1904. 


238    LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 

Possibilities  of  Single-Phase  Currents  in  Electric  Power  Transmission. 
—  Ballard  and  Sprout.  Transactions  Pacific  Coast  Transmission  Associa- 
tion, San  Francisco,  July,  1904. 

Medium  Span  Line  Construction.  —  Copeland.  Transactions  Pacific 
Coast  Transmission  Association,  San  Francisco,  July,  1904. 

Resonance  in  Aerial  Systems.  —  Physical  Review,  New  York,  Vol.  18, 
pp.  200-208. 

Surges  in  Transmission  Circuits.  —  Kennelly.  Electrical  World  and 
Engineer,  New  York,  Nov.  23,  1901,  p.  847. 

Atmospheric  Losses  on  High- Voltage  Lines.  —  Scott.  Transactions 
American  Institute  Electrical  Engineers,  Vol.  15,  p.  531. 

High-Power  Surges  in  Electric  Distribution  Systems  of  Great  Mag- 
nitude. —  Steinmetz.  Proceedings  American  Institute  Electrical  Engineers, 
Vol.  24,  p.  575. 

An  Experimental  Study  of  the  Rise  of  Potential  on  Commercial 
Transmission  Lines  Due  to  Static  Disturbances.  — Thomas.  Proceedings 
American  Institute  Electrical  Engineers,  Vol.  24,  p.  705. 

The  Conductivity  of  the  Atmosphere  at  High  Voltages.  —  Ryan. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  21,  p.  275. 

Guard  Wires  for  Transmission  Lines.  —  Electrical  Review,  Jan.  16, 
1904. 

Losses  by  Electrostatic  Discharge  on  High-Tension  Lines.  —  Electrical 
World  and  Engineer,  July  21,  1900,  p.  91. 

On  the  Mechanism  of  Electric  Power  Transmission.  —  Electrical  World 
and  Engineer,  New  York,  Oct.  24,  1903,  p.  673. 

Drop  in  Alternating-Current  Lines.  —  Mershon.  American  Electrician, 
New  York,  June,  1897. 


CHAPTER    VII 
TRANSFORMERS 

A  TRANSFORMER  is  an  alternating-current  device  for  chang- 
ing electric  energy  of  one  electromotive  force  into  the  same 
electric  energy  at  a  different  electromotive  force.  It  con- 
sists of  one  magnetic  circuit  and  two  electric  circuits,  which 
are  so  interlinked  with  it  that  current  traversing  the  pri- 
mary electrical  circuit  sets  up  an  alternating  flux  in  the  mag- 
netic circuit  which  induces  an  alternating  E.M.F.  in  the 
secondary  circuit.  The  value  of  the  alternating  E.M.F.  so 
induced  is  dependent  upon  the  ratio  of  the  numbers  of 
turns  in  the  primary  and  secondary  windings.  Hence,  the 
ratio  of  transformation  is  the  ratio  of  the  number  of  turns 
in  the  secondary  to  the  number  of  turns  in  the  primary. 

If  this  ratio  is  greater  than  unity,  the  transformer  is 
termed  a  "step-up"  transformer,  for  the  reason  that  it  de- 
livers energy  at  a  higher  potential  than  it  is  received.  If 
this  ratio  is  less  than  unity,  the  transformer  becomes  a 
"step-down"  translating  device,  since  it  delivers  energy  at 
a  lower  pressure  than  the  primary  received  pressure.  It  is 
obvious  that  in  high-tension  transmission  of  power  the 
step-up  transformer  finds  its  principal  use  at  the  generating 
end,  owing  to  the  limited  potential  which  alternators  are 
capable  of  giving,  15,000  volts  being  the  highest  pressure 
for  which  commercial  alternators  have  been  wound  up  to 
the  time  of  writing. 

The  step-down  type  is  used  at  the  receiving  points  in  a 
circuit  where  currents  of  particular  potentials  afe  necessary 

239 


240    LONG-DISTANCE    ELECTRIC    POWER    TRANSMISSION 

for  the  peculiar  characters  of  apparatus  in  use  on  distribu- 
tion circuits. 

Losses  in  Transformers.  —  Transformer  losses  are  made 
up  of  (i)  Resistance  of  the  electric  circuits;  (2)  hysteresis 
in  the  iron ;  (3)  eddy  currents  in  the  iron.  These  losses 
are  divided  into  "  copper  "  and  "  core  "  losses.  The  copper 
loss  is  due  to  the  resistance  of  the  primary  and  secondary 
windings,  while  core  losses  are  those  due" to  hysteresis  and 
eddy  currents  in  the  iron  of  the  magnetic  circuit.  Copper 
losses  also  properly  include  eddy  current  losses,  but  such 
losses  are  in  most  cases  small  enough  to  be  considered 
negligible  or  else  are  combined  with  the  eddy  current 
losses  in  the  core. 

The  magnitude  of  the  copper  loss  is  equal  to  the  product 
of  the  square  of  the  current  times  the  ohmic  resistance  of 
the  wire.  Calling  the  copper  loss  in  watts  Pc ;  Ip  the  cur- 
rent in  the  primary,  and  Is  the  current  in  the  secondary ; 
and  Rp  and  Rs  the  primary  and  secondary  resistances  re- 
spectively, then 

p  —  /2>?  -4-  np 

-1  c  —  Jp  YVp     i     Js  Yls 

from  which  it  is  evident  that  the  copper  loss  varies  as  the 
square  of  the  load  in  amperes. 

The  copper  loss  also  depends  largely  on  the  design  of  the 
transformer  and  the  conditions  of  its  operation.  A  well- 
designed  transformer  of  one  kilowatt  output  will  have  a 
copper  loss  of  from  2.5  to  3  per  cent.  For  100  kilowatt 
sizes  the  copper  loss  is  approximately  i  per  cent  of  the 
output. 

Copper  losses  increase  with  the  resistance,  and  the  re- 
sistance increasing  with  rise  of  temperature  makes  the.  loss 
larger  when  the  transformer  becomes  heated  by  the  current 
or  by  extraneous  sources  of  heat.  The  permissible  rise  in 


TRANSFORMERS  24! 

temperature  of  a  transformer  is  50°  C.  above  the  surround- 
ing air,  according  to  the  American  Institute  of  Electrical 
Engineers'  standard  code.  The  resistance  of  the  windings 
of  a  transformer  increases  about  0.004  ohm  for  each  degree 
rise  of  temperature. 

Copper  losses  affect  a  transformer  in  three  ways  :  (i) 
The  efficiency  is  reduced  ;  (2)  the  resistance  gives  rise  to 
heat  which  may  damage  the  insulation  ;  (3)  if  of  the 
constant  potential  type  the  regulation  of  the  transformer 
is  seriously  affected. 

Hysteresis  Loss.  —  A  certain  number  of  watts  are  neces- 
sary to  carry  the  iron  through  cyclic  changes  of  magnetiz- 
ation, causing  a  loss  of  energy  which  by  Steinmetz's 
equation  is, 


in  which 

JPh  =  loss  in  watts. 

V=  volume  of  core  in  cubic  centimeters. 
f=  frequency  (cycles  per  second). 
jJV=  a  hysteretic  constant. 
Bm  =  maximum  flux  density  per  square  centimeter. 

That  component  of  the  impressed  E.M.F.  which  is  neces- 
sary to  overcome  the  hysteretic  loss  is 

P       F* 
**=/,' 

and  is  in  phase  with  Ip. 

Core  losses  differ  from  copper  losses  in  that  they  are 
nearly  constant  for  all  loads,  while  the  latter  vary  as  the 
square  of  the  load.  (In  the  constant-current  type  of  trans- 
former the  converse  holds  true,  i.e.,  the  copper  loss  in  the 
secondary  is  constant,  while  the  iron  loss  varies  with 
the  load.) 


242     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

The  magnitude  of  the  core  loss  is  also  governed  by  the 
shape  of  the  impressed  E.M.F.  wave,  a  peaked  wave  form 
giving  a  slightly  lower  core  loss  than  a  flat -topped  wave.  Be- 
yond a  definite  limit,  however,  the  wave  form  may  be  so  flat 
that  the  core  loss  may  be  greater  than  that  which  would 
be  given  by  a  true  sine  curve  E.M.F. 

In  the  best  types  of  commercial  transformers  the  core 
loss  for  60  cycles  may  be  about  70  per  cent  hysteresis 
and  30  per  cent  eddy  current  loss.  At  125  cycles  it  will 
average  55  per  cent  hysteresis  and  45  per  cent  eddy  cur- 
rent loss. 

In  most  commercial  transformers  the  copper  and  core 
losses  are  almost  equal  at  full  load.  In  cases  where  constant 
voltage  is  imperative,  or  when  the  transformer  is  operated 
constantly  under  heavy  load,  the  copper  loss  is  frequently 
reduced  at  the  expense  of  the  iron  loss. 

Eddy  or  Foucault  Current  Losses.  —  These  are  caused  by 
small  currents  eddying  in  the  iron  of  the  transformer.  The 
E.M.F.  giving  rise  to  eddy  currents  is  in  phase  with  the 
counter  E.M.F.  of  the  primary,  since  both  are  due  to  the 
same  flux. 

-These  eddy  currents  cause  a  loss  of  energy  due  to  the 
heating  which  they  produce  in  the  iron.  To  reduce  this 
loss  to  a  minimum  the  cores  of  transformers  are  constructed 
of  thin  laminae  of  iron,  which  are  japanned  or  lacquered  on 
each  side.  In  the  construction  of  a  transformer  these 
laminae  are  so  placed  that  they  are  transverse  to  the  direc- 
tion of  flow  of  the  Foucault  currents,  but  are  longitudinal 
to  the  path  of  the  magnetic  flux. 

The  loss  in  watts  from  Foucault  currents  is 

P.  = 


TRANSFORMERS  243 

where 

Pe  =5  loss  in  watts. 
b  =  constant  depending  upon  the  specific  resistance  of 

.    A-Tl, 

the  iron. 

z>  ==  volume  of  the  iron  in  cubic  centimeters. 
f=  frequency  (cycles  per  second). 
t  =  thickness  of  the  laminae  in  centimeters. 
Bm  =  maximum  flux  density  per  square  centimeter. 

Eddy  current  losses  are  for  all  practical  considerations 
independent  of  the  load. 

Capacity  of  Transformers.  —  The  maximum  output  for 
which  transformers  can  be  designed  is  limited  by  several 
necessary  conditions  of  operation.  When  the  secondary 
current  is  increased  the  secondary  E.M.F.  of  the  trans- 
former decreases,  and  the  energy  output  increases  with  the 
current,  and  becomes  a  maximum.  Thus  the  maximum 
power  output  becomes  the  maximum  limit  to  the  capacity 
of  the  transformer.  But  under  commercial  conditions  the 
capacity  of  a  transformer  is  limited  to  a  considerably  smaller 
value  than  this  maximum  capacity  since  : 

(1)  If  the  rise  of  temperature  is  not  kept  within  a  cer- 
tain limit,  damage  to  insulation  will  occur  and  breakdowns 
are  liable  to  ensue. 

(2)  In   practice   it    is   generally  essential  that  constant 
secondary  E.M.F.  be  maintained. 

(3)  At    excessive   outputs   transformer   efficiencies   are 
greatly  reduced. 

The  radiation  surface  per  watt  per  degree  rise  of  temper- 
ature of  small  transformers  is  relatively  large,  and  their  out- 
put is,  in  general,  limited  only  by  the  requirements  of  close 
regulation.  In  large  transformers  the  radiating  surface  per 
watt  per  degree  rise  of  temperature  is  relatively  small,  and 


244    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

their  capacity  is  hence  limited  by  the  allowable  rise  in 
temperature. 

The  larger  the  output  of  transformers  up  to  a  certain 
limit,  the  closer  is  their  regulation  and  the  higher  their 
efficiency. 

The  capacities  of  transformers  used  in  high-tension 
practice  vary  from  a  few  kilowatts  up  to  as  high  as  7,500 
kilowatts,  which  is  the  largest  size  that  has  been  thus  far 
designed  for  commercial  operation. 

Efficiencies  of  Transformers.  —  The  efficiency  of  a  trans- 
former is  the  ratio  of  its  net  power  input  to  the  gross  power 
output  ;  or,  in  other  words,  it  is  the  ratio  of  the  power  out- 
put to  the  power  input  plus  all  losses. 

Hence  the  efficiency  of  a  transformer  is 


where  Es  is  the  difference  of  potential  at  the  secondary 
terminals,  and  Is  is  the  current  in  the  secondary  ;  and  Ph, 
Pc,  and  Pe  are  the  losses  in  watts  due  to  hysteresis,  re- 
sistance, and  eddy  currents  respectively. 

In  large  transformers  used  in  high-tension  practice,  the 
denominator  of  the  efficiency  equation  is  also  increased  by 
the  power  consumed  by  the  device  employed  in  keeping 
down  its  temperature,  such  as  the  energy  consumed  in 
running  blowers  for  air-blast  transformers,  and  in  operating 
the  motor-driven  pumps  for  oil  or  water-cooled  trans- 
formers. 

In  cases  where  one  blower  or  other  cooling  apparatus 
supplies  a  bank  of  transformers,  allowance  should  be  made 
for  the  percentage  of  energy  supplied  to  each  in  keeping 
it  cool. 

Since  transformer  losses  are    largely  governed  by  the 


TRANSFORMERS 


245 


temperature,  the  efficiency  can  only  be  accurately  deter- 
mined by  bearing  in  mind  some  definite  temperature 
(usually  25°  C). 

The  all-day  efficiency  of  a  transformer  is  the  ratio  of  the 
energy  output  to  the  energy  input  during  twenty-four  hours. 
In  practice  this  efficiency  is  calculated  on  the  assumption  of 
nineteen  hours  of  no  load  and  five  hours  of  full  load.  This 
applies  only  to  lighting  transformers. 


90 
80 

f 

^ 

/' 

TABLEOF  EFFICIENCIES 

IJfc  LOAD  =  98.  2% 
11/4         '      =98.29% 
FULL        >      =98.32% 
»/4         •       =93.24% 
1/2          .       =97.88% 
1/4          '       =96.43%       - 

/ 

X 

/ 

^ 

c 

& 
30 

<^ 

P 

x 

x 

1 

_<^-«-' 

^-^ 

•^ 

X 

- 

—  =rrr 

—        - 

..  • 

^.    -*^ 

m" 

DN  LOJ 

s 

-—  ^ 

^^ 

^^ 

e.^^ 

,0 

0 

•r-..,- 

—        — 

_—  

.^  ' 

^--> 

^^^^ 

_L 

2.5 


125 


150 


50  75  tOO 

Per  Cent  Load 

Fig.  in.    Efficiency  Curves  of  a  550  K.W.  Transformer 

The  efficiency  of  a  transformer  is  always  measured  at 
non-inductive  load  and  at  the  rated  frequency,  unless  other- 
wise specified.  Fig.  in  shows  efficiency  curves  of  a  550 
k.w.  transformer. 

Testing  of  Transformers.  —  It  is  generally  necessary  to 
make  a  certain  number  of  tests  upon  a  transformer  to 
ascertain  whether  it  is  fulfilling  the  required  specifications 
and  giving  its  rated  efficiency.  The  tests  usually  made 
have  for  their  purpose  determination  of  the  following  val- 


246     LONG-DISTANCE  ELECTRIC    POWER   TRANSMISSION 

ues :  (i)  Core  Loss  and  Leakage  Currents;  (2)  Copper 
Loss;  (3)  Resistance;  (4)  Impedance;  (5)  Heating;  (6) 
Insulation  ;  (7)  Efficiency. 

In  determining  the  core  loss  and  leakage  current,  an  al- 
ternating current  of  the  rated  secondary  pressure  and  fre- 
quency is  applied  to  the  secondary  terminals,  and  an 
ammeter  and  wattmeter  are  connected  in  the  circuit  to  read 
the  leakage  current  and  core  loss  respectively.  To  ascer- 
tain the  leakage  current  the  reading  of  the  ammeter  should 
be  divided  by  the  ratio  of  transformation.  From  the  data 
obtained  in  this  test  the  no-load  power  factor  is  readily 
calculated. 


D.  C.  Ammeter 
Fig.  iia.    Connections  for  Scott  Method  of  Hysteresis  Measurement 

Fig.  1 12  shows  the  connections  for  applying  C.  F.  Scott's 
method  of  measuring  the  hysteresis  loss  in  large  trans- 
formers. When  a  direct  current  is  sent  through  the  low- 
tension  winding  a  magnetic  field  is  set  up  in  the  iron.  With 
a  gradual  increase  or  decrease  of  current,  the  strength  of 
the  magnetic  field  will  be  proportionately  increased  or 
decreased,  and  this  varying  field  induces  an  E.M.F.  in  the 
transformer  winding  which  is  measured  by  the  voltmeter 
across  the  high-tension  terminals.  With  a  uniform  rate  of 
change  in  the  magnetic  field  there  is  a  constant  E.M.F. 
generated  in  the  winding,  and  the  voltmeter  pointer  remains 
stationary. 


TRANSFORMERS 


247 


MAXIMUM  INDUCTION  1O26O 
HYSTERESIS  LOSS 
PER  CYCLE,   PER 
CD.  CM.  OF  IRON  3958  ERGS 
HYSTERETIC  CONSTANT 
.00152 


Commencing  with  zero  current  the  resistance  is  cut  out 
in  such  steps  as  will  give  a  steady  deflection  of  the  volt- 
meter. As  soon  as  the  maximum  desired  induction  is  at- 
tained the  voltmeter  is  reversed  and  the  current  gradually 
decreased  to  zero.  The  current  is  then  reversed  and  gradu- 
ally increased  to  a 
negative  maxi- 
mum ;  then  the 
voltmeter  is  again 
reversed  and  the 
current  decreased 
to  zero,  complet- 
ing the  cycle.  It 
is  necessary  to 
bring  the  iron  "in- 
to step "  before 
making  readings, 
by  running  it 
through  several 
complete  cycles. 

Fig.  113,  hys- 
teresis curve  of 
a  2,250  kilowatt 
transformer,  shows 
the  curve  of  hyster- 
esis loss  of  a  2,250 

kilowatt  three-phase  twenty-five  cycle  Westinghouse  trans- 
former, and  Fig.  114  shows  the  efficiencies  at  various  loads 
of  the  same  transformer. 

The  copper  loss  is  determined  from  the  measured  resist- 
ance, as  given  by  the  formula  on  page  240. 

The  resistance  of  the  coils  is  most  accurately  measured 


Fig.  113.  Hysteresis  Curve  of  a  2,250  K.W.  Transformer 


248     LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 

by  the  drop  in  potential  method,  which  consists  in  measur- 
ing the  volts  drop  between  the  terminals  of  a  winding  with 
given  currents,  from  which  the  resistance  is  calculated  by 
Ohm's  Law.  In  making  this  test  on  large  transformers, 
Peck  has  modified  the  drop  in  potential  method  to  safeguard 
the  measuring  instruments  against  dangerous  pressures. 
When  direct  current  is  sent  through  a  transformer  winding 
a  magnetic  field  is  induced  in  the  iron  ;  small  current  vari- 


EFFICIENCY  AT 

DIFFERENT  LOADS 

1  V2  LOAD  98.5  % 

1'/4LOAD  98.59% 

FULL  LOAD  93.63% 

3/4  LOAD  98.6$ 

1/2  LOAD  98.2% 

V4  LOAD  97.2% 

VioLOAD  93.7% 

REGULATION 

NON     IND.  LOAD  .76% 

!0%  POWER  FACTOR 


0        10      20       30      40      50      60      70      80      90     100     110    120    130    140   150 
PER  CENT  OF  FULL  LOAD 

Fig.  114.    Efficiency  Curve  of  a  2,250  Kilowatt  Transformer 

ations  will  produce  variations  in  the  strength  of  the  mag- 
netic field,  which  may  set  up  sufficiently  high  E.M.F.'s  in 
the  transformer  windings  to  injure  the  measuring  instru- 
ments. In  Peck's  method  one  winding  is  short  circuited 
to  obviate  this  danger.  When  a  sudden  change  occurs  iri 
the  magnetic  field  a  current  is  induced  in  the  short-circuited 
winding,  which  opposes  the  change  in  the  strength  of  the 
field.  In  other  words,  the  short-circuited  winding  acts  as 


TRANSFORMERS 


249 


a  choke  coil  to  suppress  sudden  variations  in  the  magnetic 
field. 

But  in  this  method  of  resistance  determination  the  field 
does  not  instantly  become  stationary,  because  it  is  damp- 
ened by  the  short-circuited  winding ;  therefore  an  appre- 
ciable length  of  time  elapses  before  the  field  reaches  its 
maximum  value. 

During  the  interval  in  which  the  field  is  increasing,  an 
E.M.F.  is  induced  in  the  transformer  winding,  which  E.M.F. 
is  in  a  direction  to  add  itself  to  the  E.M.F.  due  to  the  re- 
sistance ;  thus  the  voltmeter  reading  is  slightly  higher 
than  it  should  be  on  account  of  the  resistance  of  the  wind- 
ing alone.  The  correct  drop  is  only  ascertained  when  the 
field  has  become  stationary. 

In  making  the  impedance  test  the  secondary  coils  of  the 
transformer  are  first  short  circuited  through  an  alternating- 
current  ammeter  of  practically  negligible  resistance,  and  a 
voltage  of  the  rated  frequency  is  impressed  upon  the 
primary  coils,  its  value  being  such  as  to  cause  the  full-load 
current  to  flow.  This  full-load  current  can  also  be  meas- 
ured on  the  primary  side,  the  secondary  being  then  short 
circuited.  (In  this  event  the  small  leakage  current  must 
be  disregarded.)  Then  the  reading  of  a  wattmeter  inserted 
in  the  primary  circuit  will  almost  correspond  to  the  copper 
loss  at  full  load  ;  while  the  reading  of  the  voltmeter  repre- 
sents the  impedance  drop,  which  is  expressed  in  per  cent 
of  the  rated  primary  pressure. 

Heating  Test.  —  The  average  temperature  of  the  coils  is 
determined  from  the  formula 

/  (rise  in  degrees  C)  =  — > 

0.004^ 

in  which  Rh  =  resistance  of  coils  when  hot,  and  R  =  re- 


250     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

sistance  at  room  temperature.  This  is  equivalent  to  divid- 
ing the  per  cent  increase  in  resistance  by  0.004.  For 
every  10  degrees  above  25°  C.  the  above  coefficient  should 
be  increased  by  1 . 5  per  cent . 

Insulation  Test. — In  making  an  insulation  test,  a  high- 
voltage  transformer  is  used,  and  the  rated  pressure  of  the 
transformer  is  applied  between  coils  and  core.  The  secon- 
dary should  be  grounded  on  the  core  when  making  a  test 
between  primary  and  secondary  of  the  core.  All  primary 
leads  should  be  connected  together  as  well  as  all  secondary 
leads  to  insure  against  undue  stresses  in  any  section  of  the 
winding. 

The  requirements  of  the  National  Board  of  Fire  Under- 
writers are :  "  That  the  insulation  of  transformers  when 
heated  shall  withstand  continuously  for  five  minutes  a  dif- 
ference of  potential  of  10,000  volts  alternating  current  be- 
tween the  primary  coils  and  the  core,  and  a  no-load  run  of 
double  voltage  for  thirty  minutes." 

Efficiency  Tests  may  be  made  by  any  one  of  several 
methods,  namely,  the  Ryan  Method  of  Instantaneous  Curves, 
the  Mordey  Method,  and  Stray  Power  Methods. 

In  the  Ryan  Method  instantaneous  contacts  are  made 
to  obtain  the  curves  of  primary  and  secondary  E.M.F.,  and 
primary  current,  the  secondary  current  being  measured  by 
an  ammeter.  From  these  curves  the  power  in  each  circuit 
is  calculated,  and  the  ratio  between  the  two  gives  the  effi- 
ciency. The  principal  advantage  of  this  method  lies  in  the 
fact  that  both  the  exact  form  and  phase  relations  of  the 
waves  are  sharply  brought  out. 

In  the  Mordey  Method  of  determining  efficiency,  the 
transformer  is  run  at  a  given  load  until  a  constant  temper, 
ature  is  reached,  as  determined  by  the  thermometer  or  by 


TRANSFORMERS 


251 


resistance  tests.  Direct  current  is  then  passed  through 
the  coils,  and  of  such  a  value  that  the  heating  effect  keeps 
the  temperature  constant.  The  direct-current  power  (El), 
which  is  readily  measured  by  a  wattmeter,  is  equal  to  the 
aggregate  losses  with  the  alternating  current. 

Stray  Power   Methods  for    determining    efficiency    are 
quite  accurate,  and  permit  of  the  individual  determination 


Fig  115.    Static  Interrupter  and  Choke  Con 

of  the  losses.  The  core  losses  are  found  from  wattmeter 
measurements  in  the  primary  circuit,  the  secondary  being 
open  circuited. 

Static  Strains  in  Transformers.  —  When  for  some  rea- 
son it  becomes  imperative  to  perform  switching  operations 
on  the  high-tension  side  of  transformers,  such  as,  for  in- 


252     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


stance,  the  opening  of  the  line  under  load  or  short  circuit, 
the  charging  of  a  dead  transformer  from  a  live  line,  or 
a  ground  on  the  line,  the  surges  or  oscillating  currents 
which  follow  may  produce  a  rise  of  potential  over  double 
that  of  the  operating  potential  of  the  line.  This  momen- 
tary rise  of  potential  will  subject  the  insulation  of  the 
primary  windings  to  a  severe  stress,  and  may  even  punc- 
ture them,  due  to  a  concentration  of  potential  in  the  layers 
of  windings  near  the  terminals. 


STATIC 
INTERRUPTER 


TRANSFORMER 


LIG'HTNING  ARRESTER 


fTO  50000 
>  LINE 


'TO  50000-VOn 
ES 


Fig. 116. 


WVWW\  ....  .  .  ...  ... * 

SERIES  GAPS 

RESISTANCE    VVWWWWWWWVMX/       / 
SHUNT  RESISTANCE 

Diagram  of  Connections  of  Static  Interrupter  and  Lightning  Arrester 


As  a  protection  against  the  severe  static  strains  to  which 
transformers  are  subjected  a  device  known  as  a  static  inter- 
rupter is  sometimes  employed. 

The  high-potential  leads  of  transformers  in  some  examples 
of  high-tension  practice  are  passed  first  through  static  inter- 
rupters, then  through  fused  circuit  breakers  on  one  leg,  and 
a  plain  knife  switch  on  the  other  leg,  connecting  thence 
to  three  heavy  bus  wires  overhead.  Fig.  1 1 5  shows  a 
static  interrupter  in  its  containing  case.  Fig.  116  shows 


TRANSFORMERS 


253 


the  connection  of  a  static  interrupter  to  protect  a  trans- 
former from  static  strains. 

Connections  of  Transformers.  —  The  various  possible 
ways  of  connecting  transformers  are  :  Single  phase,  two- 
phase,  three-phase  star  or  Y,  three-phase  delta,  three-phase 
T,  three-phase  V,  two-phase,  —  three-phase,  three-phase 
star  and  delta. 

Since  transmission  of  electrical  power  over  long  distances 
is  practically  confined  to  two-phase  and  three-phase  current, 
with  either  one  or  the  other  distributing  it,  only  the  two- 
and  three-phase  connections  will  here  be  considered. 

Fig.  117  shows  a  delta-connected  primary  and  secondary. 


Fig.  117. 


Three-Phase  Delta  Connection  1,000  to  10,000  Volts.    Maximum 
Strain  to  Ground  10,000  Volts 


The  use  of  A  or  Y  connections  of  transformers  is  de- 
pendent upon  the  peculiar  conditions  of  operation  of  the 
transmission  line,  the  use  or  non-use  of  grounded  neutrals, 
and  the  considerations  of  economy  in  translating  devices 
and  line  construction. 

If  three-phase  transmission  is  adopted,  with  three  raising 
transformers  connected  in  Y  fashion,  each  of  the  trans- 
formers must  be  wound  for  -~,  or  approximately  58  per 

^3 
cent  of  the  line  voltage  and  for  total  line  current. 

When  connected  in  A  each  transformer  must  supply  the 


254      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

full-line  pressure,  and  58  per  cent  of  the  current  per  line 
wire.  Hence  the  required  number  of  turns  in  the  winding 
of  a  F-connected  transformer  is  only  58  per  cent  of  that 
required  by  a  A-connected  one,  with  a  cross-section  of  con- 
ductors proportionately  greater.  The  increased  number 
of  turns  with  their  additional  quantity  of  insulation,  and  the 
extra  care  that  needs  to  be  carried  out  in  the  construction 
of  numerous  coils  and  layers,  make  a  much  more  expensive 
transformer  for  A  connection.  The  dimensions  are  also 
somewhat  increased  when  A  connection  is  selected. 

In  general,  Y  connection  possesses  the  advantage  in 
both  size  and  cost  over  A,  when  the  transformers  are  of 
small  output  at  high  potential.  But  Y  connection  necessi- 
tates the  employment  of  three  transformers,  and  if  an  acci- 
dent happens  to  one,  the  others  are  also  put  out  of  service 
thereby.  If  A  connected,  the  disabled  transformer  can  be 
cut  out  and  the  other  two  made  to  furnish  three-phase 
energy  up  to  their  maximum  output,  which  is  two  thirds 
of  the  maximum  capacity  of  the  three. 

When  the  neutral  or  common  point  of  junction  of  F-con- 
nected transformers  is  grounded  the  potential  between 
coils  and  core  cannot  rise  above  58  per  cent  of  the  line 
potential,  and  a  possible  reduction  in  insulation  between 
core  and  coils  is  feasible.  But  economy  in  insulation  gained 
by  a  grounded  neutral  is  practicable  only  in  the  case  of 
small  transformers,  since  with  given  voltages  the  space 
occupied  by  insulation  is  relatively  larger  in  a  small  trans- 
former. 

The  main  advantages  offered  by  A  and  F  connections 
may  be  thus  summed  up:  (i)  The  use  of  F-connected 
transformers  with  grounded  neutral  is  more  economical,  and 
is  generally  selected  on  this  score.  Without  a  grounded 


TRANSFORMERS  255 

neutral  its  advantage  is  questionable.  (2)  If  the  amount 
of  transmitted  energy  is  large,  and  the  system  supplies  a 
large  number  of  widely  scattered  apparatus,  the  use  of  A- 
connected  transformers  is  preferable,  since  it  obviates  the 
danger  of  possible  rises  of  voltage  from  various  operating 
causes.  With  F-connected  transformers  greater  precau- 
tions must  be  adopted,  such  as,  for  instance,  the  use  of 
automatic  circuit  breakers  which  will  open  all  legs  of  the 
circuits  at  the  same  time  ;  else  a  serious  liability  of  burn- 
outs on  sound  transformers  will  occur  when  one  transformer 
is  disabled. 

Many  large  transmission  systems  employ  F-connected 
transformers  in  whole  or  in  part,  while  others  use  A  connec- 
tions, or  a  mixed  A  and  F,  and  in  most  instances  with  equally 
satisfactory  operation. 

Grounding  of  Transformer  Secondaries. — The  ground- 
ing of  the  secondary  or  low-tension  circuit  of  transformers 
possesses  the  following  advantages  : 

(1)  If  one  leg  of  the  circuit  is  properly  grounded,  the 
maximum   difference  of  potential  between  any  secondary 
lead  and  ground  cannot  exceed  the  voltage  required  by  the 
apparatus  in  the  secondary  circuit,  because  in  the  event  of 
a  breakdown  between  primary  and  secondary  the  current 
has  a  path  to  ground  through  the  grounded  secondary  lead. 

(2)  If  the  secondary  circuit  is  effectively  grounded  an 
accidental    cross  between  primary  and  secondary  circuits 
will  result  in  the  blowing  of  the  primary  fuse,  or  fuses  of 
the  transformer,  and  thus  serve  as  a  warning  to  the  station 
attendants  of  the  dangerous  conditions  of  the  distributing 
circuit.     Thus,  a  grounded  secondary  will  protect  both  life 
and  property. 

The  disadvantages  of  a  grounded    secondary  are  :    (i) 


256     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

Grounding  imposes  severe  strains  upon  transformer  insula- 
tion in  case  of  static  disturbances  to  the  line.  Such  strains 
are  more  pronounced  during  lightning  storms  and  may  cause 
a  complete  breakdown  of  the  transformer.  (2)  Aerial  lines 
grounded  on  poles  are  liable  to  dangers  from  high-tension 
crosses.  (3)  Grounded  secondaries  are  liable  to  cause  fires, 
especially  when  a  service  wire  is  accidentally  grounded  or 
becomes  crossed  with  telegraph  or  telephone  wires,  which 
may  be  blown  down  by  heavy  wind  storms.  The  fire  hazard 
from  grounded  secondaries  is,  however,  greatly  minimized  if 
proper  precautions  be  taken  to  make  an  effective  ground. 

The  protection  to  both  life  and  property  and  other  advan- 
tageous features  gained  by  grounded  secondaries  are  far 
more  important  than  the  admitted  objections  ;  and  the  best 
practice  in  cases  where  a  mixed  power  and  lighting  load,  or 
a  lighting  load  only  is  supplied,  is  to  ground  the  secondary 
at  its  middle  or  neutral  point. 

Methods  of  Installation.  —  The  method  of  transformer 
installation  adopted  is  mainly  dependent  upon  the  particu- 
lar operating  conditions,  the  capacity  of  the  plant,  and  the 
potential  employed  in  transmission. 

American  high-tension  transformer  practice  has  resolved 
itself  to  the  following  general  methods  of  installation  : 

(1)  In  the  power  house  on  the  main  floor,  or  on  the  gal- 
lery floor,  or  in  separate  masonry  or  concrete  cells. 

(2)  In  a  separate  or  transformer  house. 

(3)  In  a  sub-station  —  " step-down"  transformers. 

(4)  In  the  basement  of  the  power  house. 

Practice  in  high-tension  transmission  as  regards  the  proper 
place  for  locating  raising  transformers  differs  considerably, 
and  in  addition  to  the  governing  factors  already  mentioned 
is  influenced  in  large  measure  by  considerations  of  economy. 


TRANSFORMERS 

In  cases  where  only  moderate  outputs  of  energy  are 
developed,  and  when  it  becomes  imperative  for  reasons  of 
economy  to  utilize  every  available  inch  of  floor  space,  the 
transforming  apparatus  should  be  located  on  the  main  floor 
of  the  generating  station,  adequate  precautions  being  taken 
to  thoroughly  insulate  it  from  the  walls  and  supporting 
material.  The  disadvantage  of  this  method  lies  principally 
in  the  element  of  danger  involved  in  placing  high-tension 
apparatus  in  close  proximity  to  the  moderate  tension  gener- 
ating apparatus. 

Current  practice  is  now  tending  towards  the  installation 
of  the  step-up  transformers  in  a  building  apart  from  the 
power  house.  The  transformer  house  is  constructed  of 
either  the  same  or  of  different  material  from  the  central 
station,  and  is  either  an  annex  of  the  main  building,  or  is 
an  entirely  separate  building  in  close  proximity.  When 
transformers  are  installed  in  a  separate  building,  the  low- 
pressure  leads  are  usually  conducted  from  the  power  house 
to  the  transformer  house  in  open  cable  ways  —  the  wires 
being  lead  covered.  In  most  instances  this  cable  way  is 
on  a  level  with  the  top  of  the  switchboard. 

Transformers  Used  in  High-Tension  Practice.  —  Two 
general  types  of  transformers  are  used  in  long-distance 
transmission  practice,  viz.,  core  type  and  shell  type. 

According  to  the  method  adopted  for  keeping  the  tern- 
perature  down,  transformers  are  classified  as  air-cooled, 
oil-cooled,  water-cooled,  and  water-cooled,  oil-insulated  trans- 
formers. 

The  selection  of  one  or  the  other  of  these  types  is  mainly 
governed  by  considerations  of  economy  in  operation  and  of 
floor  space.  The  air-cooled,  or  air-blast  transformer  pos- 
sesses the  advantage  of  being  able  to  quickly  and  effec- 


258    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

lively  radiate  its  heat ;  and  hence  all  of  its  coils  are  kept 
at  a  nearly  uniform  temperature,  thus  avoiding  all  danger 
from  charring  of  insulation  and  possible  burn-outs.  The 
air-cooled  type  is,  however,  more  expensive  to  maintain  than 
the  oil-cooled  kind,  except  in  cases  where  a  bank  of  trans- 
formers is  supplied  by  one  blower.  The  air-blast  type  is 
principally  used  on  circuits  under  three  kilovolts.  The  oil- 
cooled  type  is  more  economical  of  operation  than  any  of  the 
several  kinds,  since  the  oil  with  which  it  is  filled  for  insula- 
tion purposes  keeps  the  windings  from  overheating.  On 
the  other  hand  the  oil-cooled  type  does  not  radiate  its  heat 
Very  rapidly,  owing  to  the  poor  heat-conducting  properties 
of  oil,  and  hence  for  a  given  output  it  must  be  of  larger 
dimensions  than  the  air-cooled  type. 

The  water-cooled,  oil-insulated  type  of  transformer  is  com- 
ing into  extensive  use  in  hydro-electric  plants,  on  account 
of  the  easy  and  effective  reduction  of  temperature  which 
is  possible  with  this  form  of  cooling.  The  water  is  kept 
in  constant  circulation  by  means  of  a  pump,  the  casing  of 
the  transformer  being  provided  with  a  series  of  pipes  run- 
ning through  the  coils,  or  else  with  a  water-jacket  between 
the  windings  and  the  outside  casing.  Since  in  most  in- 
stances transformers  used  in  high-tension  transmission  are 
of  sufficient  size  to  permit  of  the  laying  of  water-pipes  in 
close  proximity  to  the  coils,  this  becomes  a  highly  efficient 
method  of  keeping  the  temperature  down  to  safe  limits. 

In  plants  where  the  level  of  the  forebay  is  about  six  feet 
below  that  of  the  transformers,  recourse  is  sometimes  made 
to  a  siphon  method  of  maintaining  circulation,  instead  of 
pumping  it  through  the  pipes.  In  this  method  of  water- 
cooling,  duplicate  main  intake  pipes  equipped  with  strainers 
are  brought  through  the  canal  wall  below  the  low-water 


TRANSFORMERS  259 

level.  The  transformer  coils  are  bridged  between  the  low- 
water  level  and  other  pipes  which  lead  several  feet  down 
to  the  tail-race.  The  intake  and  discharge  pipes  are  con- 
nected by  a  valve,  which  permits  water  to  flow  directly 
through  the  discharge-pipe  vents,  and  so  creates  a  vacuum. 
When  this  valve  is  closed  water  is  at  once  siphoned  through 
the  transformers.  Thiis  a  constant  supply  of  water  can  be 
maintained  through  the  coils,  and  with  no  expense  other 
than  the  initial  cost  of  installing  the  siphoning  apparatus. 
.  A  common  vacuum  gauge  is  generally  used  to  indicate  the 
condition  of  the  vacuum,  the  discharge  pipe  of  each  trans- 
former being  fitted  with  a  small  brass  pipe  about  12  inches 
long,  and  -|  inches  in  diameter  at  one  end  and  ij  inches 
in  diameter  at  the  other  end.  A  single  mercury  U  tube, 
connected  between  the  central  small  diameter  pipe  and  its 
upper  end,  affords  an  accurate  indication  of  the  water  circu- 
lating through  the  transformer.  The  quantity  of  water 
required  to  keep  the  temperature  of  transformers  down  to 
reasonable  limits  is  about  0.4  gallon  per  minute  for  a  75 
kw.  size,  about  one  gallon  per  minute  for  a  500  kw.  size, 
and  approximately  1 . 5  gallons  per  minute  for  a  i  ,000  kw. 
transformer. 

All  types  of  artificially  cooled  transformers  are  open  to 
the  objection  that  if  the  blowing  or  pumping  apparatus  used 
to  cool  them  should  become  disabled  the  transformers 
would  also  be  put  out  of  commission,  or  be  liable  to  burn 
out  from  overheating. 

(3)  Installation  of  transformers  in  sub-stations.  When 
the  transmission  voltage  must  be  reduced  to  a  value  suitable 
for  the  operation  of  motors,  converters,  lights,  or  other 
apparatus  along  the  line  or  at  the  main  distributing  point 
of  the  circuit,  the  step-down  transformers  are  usually  in- 


260     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

stalled  in  sub-stations,  located  as  near  as  possible  to  the 
apparatus  to  be  supplied. 


Figo  H3.    A  a, 750  Kilowatt  Air-Ulasi  Transformer 

Transformers    installed    in    sub-stations    are    generally 
"banked"  in  parallel,  and  connected  so  that  when  the  load 


TRANSFORMERS  26l 

is  light  only  one  transformer  is  connected  in  circuit,  the 
primaries  of  the  others  being  open  circuited.  As  the  load 
increases  the  other  transformers  are  gradually  cut  in  ;  in 


Fig.  119.    Construction  of  Air-Blast  Transformer 

this  way  the  core  losses  are  kept  in  fair  proportion  to  the 
useful  energy. 

The  installation  of  high-tension  transformers  in  buildings 
other  than  those  that  are  intended  for  electrical  apparatus 
only  is  now  prohibited  by  the  underwriters'  rules. 


262     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

Fig.  118  shows  a  2,750  kilowatt  Westinghouse  air-blast 
transformer  of  the  shell  type,  and  Fig.  119  illustrates  the 
construction  of  this  transformer,  showing  the  ventilating 
ducts  in  the  core.  The  windings  of  both  primary  and 
secondary  are  divided  into  a  number  of  flat  coils,  cotton 


•Pr 


Fig.  120.    An  800  Kilowatt,  Oil-Insulated,  Water-Cooled  Transformer 

covered.  The  primary  is  made  up  of  flat  copper  strips 
consisting  of  one  turn  per  layer.  The  coils  are  each 
separately  insulated,  and  the  space  between  each  is  filled 


TRANSFORMERS 


Fig.  iai.    A  50,000  Volt  Water-Cooled  Transformer 

with  heavy  insulation.  Each  layer  of  coils  is  separated  from 
the  other  by  a  strip  of  a  special,  high-resistance  insulating 
material,  while  the  completely  assembled  coil  is  incased  in  a 


264    LONG-DISTANCE    ELECTRIC   POWER   TRANSMISSION 

built-up  insulation  of  high  dielectric  strength  and  moisture- 
proof  character.  The  secondary  is  wound  in  a  similar 
manner,  of  rectangular  cross-section  copper  conductors. 
In  cases  where  large  currents  are  taken  from  the  secondary, 
the  winding  consists  of  several  conductors  in  parallel. 

Fig.  1 20  shows  an  800  kw.  Stanley,  oil-insulated,  water- 
cooled  transformer  of  the  shell  type,  and  illustrates  the 
method  of  winding  employed.  The  one  here  shown  is 
wound  to  give  a  secondary  E.M.F.  of  34,675  volts.  The 
primary  is  divided  into  sixteen  coils  and  the  secondary  into 
eight  coils.  Each  primary  coil  is  made  up  of  73.5  turns  of 
copper  strip,  one  turn  per  layer,  with  three  layers  in  parallel. 
Two  of  the  primary  coils  are  placed  in  position  with  a  sheet 
of  micanite  between  them  on  the  core,  and  the  groups 
alternate  or  are  sandwiched  in  between  the  secondary  coils 
—  a  secondary  between  two  primaries.  The  object  of  this 
mode  of  construction  is  to  permit  of  ample  insulation,  and 
also  to  oblige  all  of  the  magnetic  flux  to  interlink  with 
all  of  the  coils. 

Fig.  121  shows  a  950  kilowatt,  50,000  volt,  Westinghouse, 
oil-insulated,  water-cooled  transformer ,  with  the  casing 
removed.  The  method  of  winding  is  essentially  the  same  as 
that  of  the  air-blast  type,  the  spread-coil  arrangement  being 
characteristic  of  both  types.  The  coils  are  spread  apart  at 
the  ends  outside  the  core  to  allow  the  oil  to  surround  each 
coil. 


TRANSFORMERS  265 


BIBLIOGRAPHY 

Alternating  Current  Machines.  —  Sheldon  and  Mason.  D.  Van  Nos- 
trand  Co.  New  York.  1903. 

The  Transformer. — Bedell.     MacMillan  Co.     New  York.     1897. 

The  Alternating  Current  Transformer.  —  Baum.  McGraw  Publish- 
ing Co.  New  York.  1903. 

High  Tension  Transformers. — Farley.  Central  Station,  New  York. 
August,  1903. 

The  Relative  Fire  Risk  of  Oil  and  Air-Blast  Transformers.  —  Rice. 
Transactions  of  American  Institute  of  Electrical  Engineers,  Vol.  21,  p.  5. 

Terminals  and  Bushings  for  High  Pressure  Transformers.  —  Moody. 
Transactions  of  American  Institute  of  Electrical  Engineers,  Vol.  21,  p.  15. 

Static  Strains  in  High  Tension  Circuits  and  the  Protection  of  Appa- 
ratus.—  Thomas.  Transactions  of  American  Institute  of  Electrical  En- 
gineers, Vol.  19,  p.  213. 

Reactance  Drop  and  Reactance  Factor  of  Transformers.  — Kennelly. 
Electrical  World  and  Engineer,  New  York,  July  20,  1901,  p.  92. 


OF  THF 

I    UNIVERSITY 

/ 

!K'\^X 


CHAPTER   VIII 
MOTORS 

SYNCHRONOUS    MOTORS 

Relation    Between    Generator  and   Motor   Speed,    Torque, 

and   Output. 

IF  an  excited  single-phase  or  polyphase  alternator  be 
brought  up  to  normal  speed  and  then  connected  to  an  alter- 
nating-current circuit  of  the  same  periodicity  and  E  M.F. 
it  will  run  as  a  motor,  and  its  speed  in  revolutions  per 
second  will  equal  the  quotient  of  the  periodicity  by  the 
number  of  pairs  of  poles.  When  operating  under  these  con- 
ditions the  motor  is  said  to  be  working  in  synchronism,  or 
its  rotor  is  revolving  at  synchronous  speed.  This  synchro- 
nous speed  is  not  literally  the  speed  of  the  generator  which 
is  supplying  the  motor  with  energy,  but  is  a  speed  which  if 
multiplied  by  the  number  of  poles  produces  a  value  equal  to 
the  alternations  of  the  generator.  Thus  a  motor  with  half 
the  number  of  poles  as  the  generator  will  have  double  its 
speed  in  revolutions  per  minute,  and  vice  versa. 

The  speed  of  a  synchronous  motor  is  independent  of  the 
pressure,  and  can  be  varied  by  varying  the  speed  of  the 
generator.  Hence,  closeness  of  regulation  of  the  prime 
mover  supplying  synchronous  motors  is  of  prime  impor- 
tance, since  the  armature  of  tjie  motor  possesses  a  fly-wheel 
property  of  sufficient  magnitude  to  consume  a  relatively 
large  amount  of  energy  without  greatly  varying  its  speed. 

266 


MOTORS  267 

Moreover,  there  will  be  an  interchange  of  currents  between 
the  motor  and  the  generator  which  will  cause  troublesome 
regulation,  and  also  diminish  the  motor  output. 

The  behavior  of  a  synchronous  motor  on  starting  is  nearly 
similar  to  that  of  the  induction  motor.  Its  torque  at  start- 
ing may  range  from  zero  to  25  or  35  per  cent  of  the  full- 
load  running  torque,  depending  mainly  on  its  design.  The 
torque  of  the  synchronous  motor  is  a  function  of  the  ter- 
minal E.M.F.  and  is  limited  by  it  chiefly. 

The  limit  to  the  output  of  a  synchronous  motor  is  the 
heating  of  the  machine.  Polyphase  synchronous  motors 
of  good  design  can  be  made  to  carry  from  three  to  five 
times  full  load.  With  further  increase  of  load  they  drop 
out  of  synchronism,  and  can  only  be  brought  into  synchro- 
nism again  by  removal  of  the  load. 

Methods  of  Starting  Synchronous  Motors.  —  The  starting 
torque  of  a  synchronous  motor  being  too  low  to  bring  it 
up  to  speed  under  load,  some  extraneous  source  of  power 
is  necessary  to  perform  this  task,  the  auxiliary  device 
being  disconnected  as  soon  as  synchronism  is  attained. 
For  this  purpose  synchronous  motors  are  generally  pro- 
vided with  induction  motors  for  starting  them,  the  capacity 
of  the  auxiliary  being  about  one-tenth  that  of  the  synchro- 
nous motor.  The  small  motor  is  usually  geared  to  the 
shaft  of  the  main  motor,  as  shown  in  Fig.  122,  which  is  an 
illustration  of  a  500  horse-power  motor. 

In  connecting  a  synchronous  motor  to  the  mains,  it  is 
essential  that  the  motor  should  not  only  be  running  at 
synchronous  speed,  but  also  that  the  phase  difference  be- 
tween the  motor  E.M.F.  and  the  impressed  voltage  should 
be  1 80  degrees.  The  determination  of  these  points  is 
accomplished  by  means  of  a  synchronizer. 


268     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

When  synchronous  motors  are  brought  up  to  speed  with- 
out the  aid  of  an  auxiliary  device,  the  method  of  starting  is 
generally  as  follows :  The  field  circuit  is  first  opened  and 
the  armature  connected  either  directly  to  the  source  of 
supply,  or  to  a  starting  compensator  which  reduces  the 
supply  E.M.F.  The  armature  windings  produce  a  mag- 


Fig.  122.    A  Synchronous  Motor  with  Auxiliary  Starting  Motor 


netizing  effect  which  sets  up  enough  flux  in  the  poles  to 
furnish  a  low  starting  torque. 

The  exciter  current  is  then  switched  on  to  the  field  and 
the  motor  gradually  brought  up  to  synchronism.  The 
starting  current  is  limited  only  by  the  impedance  of  the 
armature  windings,  and  may  have  a  value  ranging  from 
150  per  cent  of  full-load  current  to  two  or  three  times  nor- 


MOTORS 


269 


mal  operating  current.  The  external  load  is  subsequently 
thrown  on  the  motor  through  the  medium  of  a  friction 
clutch  or  equivalent  appliances  which  cause  the  load  to 
be  gradually  applied  to  the  motor  after  it  has  attained 
synchronous  speed. 


Fig.  123.     Synchronous  Motor  Belted  to  Shafting 

Fig.  123  illustrates  a  synchronous  motor  belted  to  a  line 
of  shafting  on  which  is  mounted  a  friction  coupling. 

The  chief  objection  to  starting  the  load  by  means  of 
friction  clutches  lies  in  the  danger  of  a  break-down  in  the 
field-coil  insulation,  due  to  the  high  pressure  generated  in 
the  field  by  the  varying  flux.  To  obviate  this  each  field 


2/0       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

coil  is  provided  with  a  break-up  switch  to  open  circuit  the 
coils  on  starting.  The  taps  or  leads  from  each  coil  are  led 
to  the  switch  blades,  —  which  are  mounted  on  an  easily 
accessible  part  of  the  motor  frame.  When  the  motor  falls 
into  step  with  the  generator,  the  switch  is  closed,  which 
puts  the  field  in  series  and  also  throws  it  in  circuit  with 
the  exciter. 

The  Use  of  Synchronous  Motors  as  Voltage  Regulators 
on  Long-Distance  Circuits.  —  On  long-distance  circuits 
containing  a  number  of  pieces  of  inductive  apparatus  in 
circuit,  not  only  is  the  power  factor  of  the  system  appreci- 
ably lowered  thereby,  but  objectionable  lagging  currents 
are  produced  in  certain  parts  of  the  system.  The  great  flexi- 
bility of  the  synchronous  motor  is  taken  advantage  of  in 
this  class  of  work  to  overcome  the  bad  effects  caused  by 
apparatus  of  inductive  character.  By  increasing  the  ex- 
citation of  a  synchronous  motor  the  power  factor  can  be 
made  equal  to  unity  for  any  load.  Likewise  an  increase  of 
exciting  current  will  give  a  proportional  increase  in  press- 
ure produced  by  the  motor,  so  that  by  a  proper  adjust- 
ment of  the  excitation,  the  E.M.F.  generated  by  the  motor 
can  be  increased  considerably  above  the  voltage  impressed 
upon  its  terminals.  When  the  operating  conditions  are 
exactly  opposite,  i.e.,  when  the  field  excitation  is  low,  the 
E.M.F.  generated  is  lower  than  the  impressed  volts. 

Under  the  first  set  of  conditions,  the  current  will  be  a 
leading  one,  while  under  the  second  it  will  lag  behind  the 
impressed  volts.  Over-exciting  a  synchronous  motor  will 
cause  it  to  behave  like  a  big  condenser  ;  and  so  operated 
it  will  provide  for  both  energy  and  wattless  components  of 
current  up  to  its  rated  output  in  amperes. 

The  amount  of  current  absorbed  by  a  synchronous  motor 


MOTORS 


271 


depends  upon  its  field  excitation,  there  being  one  value  of 
exciting  current  for  which  the  current  in  the  armature  is 
a  minimum. 

These  properties  of  the  synchronous  motor  make  it  a 
valuable  piece  of  apparatus  for  regulative  purposes,  outside 
of  its  motor  functions,  since  by  producing  a  phase  dis- 


2000 


1000 


5 
100 


10 
200 


15 

300 


TION  AND  AIR   LC 
ATJION 

20  25 

400  500 


30  EXCITATION 


600    KW.fpW.FR  I, 


ABSORBED 

Fig.  124.    Curves  of  525  H.P.  Three-Phase  Synchronous  Motor 

placement  between  its  current  and  voltage,  the  reactance 
caused  by  the  inductance  of  the  line  and  inductive  appara- 
tus can  be  wholly  or  partly  neutralized.  Hence,  by  prop- 
erly distributing  such  motors  along  a  circuit  a  low  power 
factor  caused  by  induction  motors,  or  apparatus  of  like 
nature,  can  be  corrected  to  any  desirable  extent. 

Another  very  valuable  feature  of  the  synchronous  motor 


272     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

is  that  in  an  emergency,  such  as  a  failure  in  the  source  of 
current  supply,  the  motor  can  be  made  to  perform  the 
function  of  a  generator  by  driving  it  from  some  extraneous 
source  of  power,  and  thus  become  the  generator  at  the 
sub-stations,  supplying  energy  to  induction  motors,  lamps, 
or  other  dead  loads  in  circuit.  In  many  stations  this  con- 
venient property  of  the  machine  is  taken  advantage  of  to 
such  an  extent  that  during  day  hours  synchronous  motors 
discharge  their  normal  functions,  while  at  night,  or  when- 
ever the  peak  of  the  load  occurs,  the  motors  are  operated 
as  generators. 

Troubles  of  Synchronous  Motors. — A  synchronous  motor, 
both  electrically  and  mechanically,  is  almost  similar  to  an 
alternator,  and  requires  the  same  auxiliary  apparatus,  such 
as  an  exciter  and  indicating  instruments.  It  is  also  gen- 
erally provided  with  a  starting  motor  or  other  device. 
Hence,  like  the  generator,  any  failure  or  breakdown  of  the 
exciting  machine  will  put  the  motor  out  of  operation. 

If  the  exciting  circuit  is  suddenly  ruptured  the  high 
E.M.F.  induced  by  the  armature  may  result  in  a  "field 
discharge,"  which  is  liable  to  puncture  the  insulation  of  the 
coils. 

Being  provided  with  moving  contacts  —  collector  rings, 
commutator,  and  brushes  —  the  usual  troubles  from  this 
source,  such  as  destructive  sparking  and  short  circuiting, 
are  liable  to  occur. 

On  starting  up,  trouble  or  injury  is  liable  to  result  from 
improper  or  unsystematic  performance  of  the  various  oper- 
ations. Thus,  synchronizing  may  be  attempted  before  the 
motor  is  in  exact  phase,  or  when  it  is  below  normal  speed. 

Should  the  load  of  a  synchronous  motor  (which  may 
possess  a  large  inertia)  be  thrown  on  too  suddenly,  the 


MOTORS  2/3 

motor  may  not  possess  a  large  enough  torque  and  fly-wheel 
capacity  to  keep  its  speed,  and  will  be  brought  to  a 
standstill. 

If  the  motor  is  stopped  by  a  failure  of  the  source  of 
current  supply,  it  will  not  start  of  its  own  accord  when  the 
current  is  restored,  but  requires  to  be  put  in  operation  by 
the  starting  motor. 

The  electrical  connection  between  generator  and  motor 
being  rigid  and  unalterable,  the  operating  current  of  the 
mctor  depends  upon  the  steadiness  or  uniformity  of  the 
frequency  of  the  supply  current,  or  in  other  words,  upon 
the  constancy  or  uniformity  of  the  generator  speed  and 
other  synchronous  motors  in  circuit. 

The  motors  endeavor  to  keep  exactly  in  step  with  the 
speed  of  the  supplying  generator.  Any  variation  of  the 
latter  tends  to  cause  a  corresponding  variation  of  motor 
speed.  This  sets  up  a  pulsation  or  vibration  on  both  sides 
of  a  mean  position  which  may  increase  to  such  an  extent 
as  to  throw  all  synchronous  apparatus  in  the  circuit  out  of 
step. 

"Pumping"  or  "hunting"  is  also  liable  to  occur  when 
the  mechanical  load  on  the  motor  is  suddenly  changed  to  a 
valfee  which  exceeds  the  limiting  torque  and  the  load  has 
considerable  inertia. 

A  synchronous  motor  is  also  liable  to  cause  trouble  or 
annoyance  by  coming  to  a  standstill  when  the  generator 
quickly  speeds  up,  due  to  the  inability  of  the  motor  to 
increase  its  speed  suddenly  without  exceeding  its  maximum 
torque.  In  the  event  of  a  short  circuit  in  the  transmission 
system,  a  synchronous  motor  may  turn  generator  and  thus 
greatly  augment  the  intensity  of  the  short  circuit  by  in- 
creasing the  line  current. 


274    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

THE  INDUCTION  MOTOR 

An  induction  motor  closely  resembles  in  its  performance 
a  direct-current  shunt-wound  motor,  the  main  points  of  dif- 
ference being  that  the  operating  current  of  the  direct-cur- 
rent motor  is  conducted  into  the  armature  by  means  of 
brushes,  while  the  operating  current  of  the  induction  motor 
is  an  induced  current,  and  that  the  induction  motor  has  no 
physical  field  magnet  poles. 

The  essential  elements  of  the  motor  are  a  primary  or 
stator  and  a  secondary  or  rotor.  The  primary  winding  in 
most  cases  is  connected  to  the  source  of  current  supply, 
and  in  addition  to  carrying  the  exciting  current  it  performs 
the  office  of  inducing  the  working  current  in  the  secondary 
conductors. 

Rotation  of  the  secondary  member  may  be  regarded  as 
being  due  to  a  rapidly  varying  magnetic  field  which  the 
revolving  member  follows.  This  shifting  magnetic  field  is 
the  resultant  of  two  or  more  alternating  magnetic  fields 
differing  in  phase. 

The  rotor  of  an  induction  motor  may  be  of  the  squirrel- 
cage  or  short-circuited  type,  or  the  variable  resistance  or 
polar  type. 

Rotors  of  the  squirrel-cage  type  are  generally  "  wound  " 
with  copper  bars  embedded  in  slots  in  a  laminated  steel 
core.  The  windings  or  inductors,  which  are  of  low  resist- 
ance, are  all  connected  in  parallel  to  short-circuited  rings 
placed  at  each  end  of  the  rotor.  Since  the  currents  induced 
in  the  inductors  are  obliged  to  flow  parallel  with  the  axis  of 
the  motor,  the  reaction  set  up  by  them  against  the  field 
rlux  is  in  a  direction  to  be  most  efficient  in  causing  rotation. 

The  short-circuited  or  squirrel-cage  type  of  motor  of 
small  inductance  possesses  the  following  features  : 


MOTORS  275 

(i)  Break-down  point  of  high  value;  (2)  moderately 
large  magnetizing  current ;  (3)  fairly  large  current  for 
starting  and  for  starting  torque  ;  (4)  moderate  percentage 
drop  in  speed;  (5)  high  power  factor ;  (6)  high  efficiency 
at  full  and  overloads. 

In  induction  motors  of  the  variable  resistance  or  polar 
type  the  rotor  is  wound  with  a  definite  series  of  coil  wind- 
ings, which  correspond  to  the  polar  windings  of  the  stator. 

The  characteristic  features  of  the  polar  or  variable  resist- 
ance type  of  induction  motor  are:  (i)  Moderate  break- 
down point ;  (2)  small  magnetizing  current ;  (3)  low 
percentage  drop  in  speed ;  (4)  torque  proportional  to  the 
starting  and  running  current ;  (5)  high  power  factor  ;  (6) 
high  efficiency  at  intermediate  and  full  loads. 

The  squirrel-cage  type  of  motor  finds  its  most  useful  field 
of  application  on  power  circuits  where  the  conditions  of  oper- 
ation call  for  low  starting  effort  and  steady  full  load.  It  is 
also  particularly  adapted  to  cases  where  the  motor  is  .required 
to  run  overloaded,  or  on  circuits  of  fluctuating  voltage. 

The  particular  sphere  of  usefulness  to  which  the  variable 
resistance  type  of  motor  is  adapted  is  on  circuits  where 
close  regulation  is  imperative,  such  as  combined  power  and 
lighting  service,  and  under  conditions  where  the  motors 
are  usually  run  underloaded. 

Operation  of  Induction  Motors.  —  Calling  the  speed  at 
which  the  magnetic  field  rotates  n^  and  the  speed  of  the 
rotor  n2,  the  relative  speed  between  any  given  inductor  on 
the  revolving  element  and  the  rotating  field  will  be  n^  —  n^ 
The  ratio  of  this  speed  to  that  of  the  revolving  field  is 
called  the  slip  ;  hence  the  slip  is 


2/6      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  value  of  the  slip  is  usually  given  as  a  certain  per  cent 
of  the  synchronous  speed,  ;/1% 

Calling  the  flux  emanating  from  any  given  north  pole  of 
the  primary  <1>  maxwells,  then  any  single  secondary  inductor 
will  have  an  effective  E.M.F.  induced  in  it  equal  to 

1. 1 1  /<£;/!  io~8, 
in  which  /  represents  the  number  of  poles. 

The  E.M.F.  so  induced  has  a  periodicity  which  differs 
from  the  periodicity  of  the  impressed  E.M.F.,  being  s  times 
the  frequency  of  the  latter. 

If  the  secondary  rotated  in  synchronism  with  the  primary 
the  secondary  frequency  would  be  zero;  if  the  secondary 
remained  stationary  the  frequency  of  its  current  would 
equal  that  of  the  current  in  the  primary. 

In  commercial  conditions  of  operation  the  periodicity  of 
the  E.M.F.  in  the  secondary  winding  is  of  low  value,  since 
the  slip  of  most  motors  is  of  small  value  (from  2  to  15  per 
cent). 

In  a  squirrel-cage  secondary  the  determination  of  current 
in  a  single  inductor  presents  considerable  difficulty,  since 
the  E.M.F.'s  in  all  the  inductors  are  of  different  magnitude 
at  any  given  instant.  It  is  also  possible  that  in  some  of  the 
windings  the  current  and  E.M.F.  may  be  flowing  in  oppo- 
site directions. 

When  an  induction  motor  is  running  without  load,  the 
speed  of  the  revolving  member  is  very  nearly  equal  to  that  of 
the  rotating  field,  being  equal  to  n^(i  —  s).  Hence,  the 
E.M.F.  generated  is  only  sufficient  to  set  up  a  current 
in  the  secondary  windings  large  enough  to  make  the  elec- 
trical power  equal  to  the  losses  in  the  iron  and  copper,  and 
those  due  to  windage  and  friction.  A  very  feeble  torque  is 
produced  by  the  magnetic  pull  of  this  current. 


MOTORS  277 

On  applying  a  mechanical  load  to  the  rotor  pulley,  a  drop 
in  speed  occurs  due  to  an  increase  in  the  slip.  With  in- 
crease of  load  the  speed  of  the  rotor  falls  further  away  from 
synchronism,  while  the  current  and  E.M.F.  therein  increase 
in  proportion,  and  the  rotor  receives  additional  increments 
of  energy  corresponding  to  the  additions  in  load.  The  force 
exerted  by  the  increased  current  exerts  a  torque  which  is 
in  proportion  to  the  increase  of  energy  —  that  is,  up  to  a 
critical  point. 

Under  varying  loads  the  magnetism  of  the  rotating  field 
which  cuts  the  rotor  inductors  varies  also  ;  and  with  in- 
crease of  slip  an  increasing  amount  of  primary  flux  passes 
between  primary  and  secondary  windings  without  cutting 
them.  The  tendency  of  the  increased  secondary  currents 
to  set  up  a  cross-magnetizing  action  causes  the  increase  in 
magnetic  leakage ;  the  effect  of  which  is  not  only  to  re- 
duce the  torque  for  an  equivalent  secondary  current,  but 
also  requires  an  increased  slip  to  give  the  same  current. 

The  curves  in  Fig.  125  exhibit  the  relation  between 
torque  and  slip  for  different  secondary  resistances.  The 
solid  lines  represent  torque,  and  the  broken  lines,  current. 
As  the  curves  show,  the  greatest  torque  which  a  motor 
can  exert  is  the  same  for  various  secondary  resistances. 
But  when  giving  this  maximum  torque,  the  rotor  speed 
differs  with  the  difference  of  resistance  in  the  rotor.  This 
characteristic  of  the  induction  motor  is  employed  to  keep 
down  the  excessive  starting  current  which  follows  when  a 
motor  is  connected  to  its  source  of  supply. 

In  Fig.  126  are  shown  the  relations  between  the  torque, 
speed,  power  factor,  current,  and  efficiency  of  a  modern 
induction  motor  working  under  average  conditions  of  prac- 
tice. With  an  increase  of  impressed  E.M.F.,  there  is  a 


2/8     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

corresponding  increase  of  magnetic  flux  interlinked  with 
the  secondary,  and  hence  a  proportional  increase  of  secon- 
dary current. 

The  torque  exerted  by  a  motor  is  proportional  to  the 
product  of  the  magnetic  flux  and  the  ampere-turns  of  the 
secondary ;  hence,  the  torque  of  an  induction  motor  varies 


860,000- - 


80  40  30  20  10 


SYNCHRONISM 


Fig.  125.    Relation  Between  Torque  and  Slip  in  Induction  Motors 

as  the  square  of  the  impressed  voltage.  From  this  it  fol- 
lows that  the  output  of  an  induction  motor  varies  when  it 
is  used  on  circuits  of  varying  voltages. 

Speed  Regulation  of  Induction  Motors.  —  Variations  in 
the  speed  of  an  induction  motor  can  be  accomplished  either 
by  varying  the  pressure  impressed  upon  the  primary,  or 
by  varying  the  resistance  in  the  rotor,  or  by  changing  the 


MOTORS 


279 


number  of  field-polar  planes  by  commutation  of  the  stator 
windings. 

The  first  two  methods  depend  upon  the  principle  that 
the  torque  of  the  motor  is  proportional  to  the  product  of 
stator  flux  and  rotor  current ;  hence  for  a  fixed  torque  the 
product  is  a  constant.  If  the  voltage  impressed  upon  the 


ROTOR   STATOR 
AMP.      AMP. 

1500     150 


cos 
1000    100  1.00 


500     50 


100  200  300  400  500  600     700  H. P. 

Fig.  126.    Relations  Between  Torque,  Speed,  Power  Factor,  Current,  and  Efficiency 


stator  is  lowered  a  reduction  of  stator  flux   and  also   of 
rotor  current  ensues.     Hence,  the  speed  of  the  motor  de-« 
creases  until  sufficient  E.M.F.  is  generated  to  give  rise  to 
a  current  which,  when  combined  with  the  diminished  flux, 
will  afford  the  original  torque. 

The  first  method  of  speed  control  —  changing  the  im- 
pressed volts  at  the  motor  terminals  —  requires  the  use  of 


28O      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

a  compensator  or  external  reactance,  and  the  motor  should 
possess  high  constant  rotor  resistance.  The  compensator 
and  its  controller  are  generally  separate  from  the  motor. 
The  former  is  fitted  with  the  requisite  number  of  taps 
from  which  leads  are  conducted  to  the  controller.  By 
manipulation  of  the  controller  handle,  a  gradual  variation 
of  the  impressed  voltage  is  effected,  which  causes  a  cor- 
responding variation  in  the  speed. 

Speed  variation  by  altering  the  resistance  is  effected  by 
inserting  resistance  in  the  rotor  circuit,  the  resistance 
being  varied  in  graduated  steps.  This  method  requires 
the  use  of  an  external  rheostat  or  controller  with  sufficient 
resistance  to  dissipate  a  goodly  amount  of  energy.  Fig. 
127  is  a  diagrammatic  representation  of  the  connections 
of  the  controlling  rheostat  of  a  three-phase  motor.  When 
the  secondary  element  revolves,  collecting  rings  are  neces- 
sary to  connect  the  windings  electrically  with  the  exter- 
nal resistance.  An  increase  of  rotor  resistance  lessens 
the  rotor  current  and  necessitates  a  drop  in  speed  to  bring 
its  value  up  to  normal,  hence  the  efficiency  of  operation  is 
lowered  by  this  method. 

A  reduction  in  impressed  voltage  results  in  a  reduction 
of  motor  capacity  or  output,  since  the  output  of  an  induc- 
tion motor  varies  as  the  square  of  the  impressed  voltage. 

Alteration  in  the  speed  of  an  induction  motor  by  chang- 
ing the  number  of  polar  planes  is  extremely  complicated, 
and  requires  a  complex  switching  apparatus  in  addition  to 
a  compensator.  The  variations  of  speed  are  also  limited 
to  full,  one  half,  and  one  quarter  speeds.  This  method  is 
occasionally  used  under  conditions  which  demand  half- 
speed  and  half-load  torque. 

Efficiency  and    Power    Factor    of    Induction   Motors.  - 
Since  the  losses  in  an  induction    motor    are  of  a  similar 


MOTORS 


28l 


kind  to  those  in  a  generator,  i.e.,  core,  copper,  and  friction 
losses,  the  efficiency  can  be  considerably  increased  by  the 
generous  use  of  both  iron  and  copper.  Efficiencies  of 
modern  induction  motors  range  from  70  to  94  per  cent, 
depending  upon  their  size  and  the  conditions  of  operation. 


Fig.  137.    Connections  of  Controlling  Rheostat  of  Three-Phase  Induction  Motor 

Motors  for  factory  and  shop  work  are  frequently  de- 
signed to  give  their  maximum  efficiency  at  about  three 
quarters  load.  This  is  due  to  the  fact  that  such  motors 
are  only  required  to  give  full  load  at  infrequent  intervals, 
the  average  working  conditions  calling  for  about  20  to  30 
per  cent  less  load  than  their  rated  output. 

The  power  factor  of  an  induction  motor  is  the  ratio  of 


2$2     LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 

the  total  current  received  to  the  energy  current,  or  the 
current  which  supplies  its  losses  and  does  the  work  at  the 
shaft.  The  apparent  efficiency  of  an  induction  motor  is 
the  product  of  the  power  factor  and  the  actual  efficiency. 

The  power  factor  of  modern  induction  motors  at  full 
load  ranges  from  75  to  92.5  per  cent,  depending  upon  their 
capacity  and  design.  Since  a  low  power  factor  is  caused 
by  magnetic  leakage,  it  is  feasible  to  improve  the  power 
factor  by  making  the  air-gap  as  short  as  is  consistent  with 
mechanical  clearance ;  also  by  reducing  magnetic  density 
in  the  iron,  which  reduces  the  magnetizing  current.  But 
applying  these  methods  and  maintaining  high  efficiency 
greatly  increases  the  cost  of  the  motor. 

Faults  of  Induction  Motors.  —  The  salient  objections  to 
the  induction  motor  are  : 

(1)  The  starting  current  at  full  load  (with  reasonable 
efficiency)  is  several  times  the  full-load  current.     This  fault 
is  characteristic,  however,  only  of  the  squirrel-cage  motor. 

(2)  The  current  consumed  in  giving  full-load  starting 
torque  may  be  from  four  to  six  times  full-load  current. 

(3)  High  starting  torque  with   moderate  starting  cur- 
rent is  obtained  at  the  expense  of  considerable,  and  not 
infrequently   cumbersome    auxiliary     apparatus,    such    as 
collector  rings,  brushes,  and  rheostat. 

(4)  Low  power  factor. 

(5)  Inflexibility  of  speed  control. 

Although  in  many  instances  the  majority  of  these  ob- 
jections to  the  induction  motor  are  valid  and  tenable,  in 
the  majority  of  cases  the  faults  are  due  either  to  the  adop- 
tion of  the  wrong  motor  for  the  conditions  desired,  or  else 
the  use  of  motors  of  bad  design. 

In  regard  to  the  first  fault,  let  us  consider  a  comparison 
between  the  variable  resistance  in  the  secondary  induction 


MOTORS  283 

motor  and  the  direct-current  shunt  motor,  started  by  an 
external  rheostat  in  its  armature  circuit.  There  is  practi- 
cally no  difference  between  the  two  as  regards  the  mode 
of  starting,  the  purpose  of  the  rheostat  in  both  cases  being 
to  prevent  the  excessive  rush  of  current  which  always 
follows  when  any  motor  is  connected  to  its  supply  circuit. 
It  is  true,  however,  that  the  drop  in  voltage  at  the  ter- 
minals of  other  apparatus  (on  account  of  this  large  starting 
current),  when  an  induction  motor  is  started  up,  is  some- 
what greater  than  the  drop  which  follows  the  connection 
of  a  direct-current  motor  to  its  source  of  supply.  In  many 
instances  such  trouble  is  brought  about  by  a  low  power 
factor,  or  by  faulty  design. 

Regarding  the  starting  torque  of  the  induction  motor,  it 
may  be  said  in  general  that  if  abnormal  means  are  adopted 
to  secure  very  high  starting  torque,  the  limit  will  be  reached 
much  earlier  with  the  direct-current  shunt-wound  motor 
than  with  the  induction  motor  of  the  type  first  considered. 

Just  as  the  direct -current  motor  may  be  started,  stopped, 
reversed,  or  run  at  high,  low,  or  intermediate  speeds,  by 
means  of  a  rheostat,  and  with  small  torque  or  large  torque, 
so  likewise  may  the  induction  motor  be  operated  under 
identically  the  same  conditions. 

This  is  equally  true  of  an  induction  motor  which  is  not 
provided  with  slip  rings,  but  has  its  speed  controlled  by 
varying  the  voltage  impressed  upon  it.  In  certain  kinds 
of  power  service,  it  is  highly  essential  that  a  motor  should 
act  as  a  constant-speed  machine  when  running  at  any  one 
of  a  large  number  of  widely  varying  speeds.  In  other 
words,  a  varying  torque  should  not  appreciably  affect  the 
speed.  Such  a  requirement  cannot  be  met  by  any  kind  of 
motor  under  purely  rheostatic  control,  under  the  cited  con- 


284     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

ditions,  since  the  torque  in  connection  with  the  resistance 
entirely  determines  the  speed  of  operation,  an  increase  of 
either  lowering  it,  and  a  decrease  of  either  raising  it. 

Induction  motors  of  recent  manufacture  have  given  a 
power  factor  when  starting  with  a  given  torque  of  prac- 
tically the  same  as  when  running  at  that  torque;  and  as 
the  full-load  power  factor  of  a  well-designed  motor  of  this 
type  may  be  as  high  as  90  per  cent,  the  power  factor  when 
carrying  a  load  requiring  full-load  torque  may  be  as  high  as 
90  per  cent. 

With"  an  induction  motor  of  the  squirrel-cage  type  there 
is  considerable  liability  of  annoying  disturbances  if  the 
motor  is  started  under  load,  or  run  below  normal  speed, 
due  to  the  low  power  factor  of  this  type  of  motor.  At  full 
speed,  however,  the  power  factor  may  be  as  high  as,  or  higher 
than,  the  power  factor  of  an  induction  motor  under  rheo- 
static  control. 

Although  the  starting  up  of  squirrel-cage  induction 
motors  gives  rise  to  more  or  less  line  disturbances,  their 
somewhat  higher  efficiency,  and  the  fact  that  circumstances 
often  arise  when  the  motor  can  be  started  under  light  load, 
render  the  objectionable  feature  nugatory. 

The  efficiency  of  an  induction  motor  is  not  entirely  de- 
pendent upon  the  power  factor  of  the  system,  it  being 
quite  feasible  to  design  a  motor  for  a  low  power  factor  and 
a  high  efficiency  or  vice  versa.  At  medium  and  light  loads 
the  efficiency  of  the  induction  motor  is  slightly  in  excess  of 
that  of  the  direct-current  motor.  At  such  loads,  however, 
the  current  consumption  of  the  induction  motor  is  slightly 
greater  than  that  of  a  direct-current  motor  of  equal  output. 
At  full  load  and  equivalent  currents  consumed  at  full  load, 
the  advantage  is  held  by  the  direct-current  machine. 


MOTORS 


28S 


Types  of  American  Induction  Motors.  —  Fig.  1 28  shows 
the  primary  of  a  500  horse-power  Westinghouse  Type  C, 


Fig.  128.    Stator  of  a  500  H.  P.  Induction  Motor 

squirrel-cage  induction  motor  designed  for  constant  speed. 
Fig.  129  shows  a  completely  assembled  150  horse-power 
Westinghouse  motor.  The  frame  of  the  motor  is  made 


286     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


Fig.  129.    A  150  H.  P.  Induction  Motor 


MOTORS  287 

of  cast  iron  divided  in  a  horizontal  plane.  The  primary 
is  built  up  of  laminated  sheet  steel  and  constitutes  a  hol- 
low cylinder  with  internal  slots  in  which  the  winding  is 
laid.  The  laminated  rings  of  which  the  cylinder  con- 
sists are  of  segmental  design  and  are  dovetailed.  These 
segments  fit  into  corresponding  slots  in  a  hollow  shell 
made  of  cast  iron,  which  is  rigidly  held  in  the  frame  of 
the  motor. 

The  winding  consists  of  copper  strap  made  into  coils 
and  bent  into  the  proper  form.  The  terminal  blocks 
through  which  current  is  supplied  to  the  motor  are  located 
on  the  side  of  the  frame.  The  rotor  is  built  up  of  lami- 
nated steel  discs,  mounted  on  a  spider.  The  rotor  induc- 
tors consist  of  rectangular  copper  bars  embedded  in 
partially  closed  slots,  all  conductors  being  short  circuited. 

Fig.  130  shows  a  General  Electric  squirrel-cage,  con- 
stant-speed motor  of  750  horse-power  capacity. 

The  Repulsion  Motor.  —  The  repulsion  type  of  alternat- 
ing-current motor  invented  by  Professor  Elihu  Thomson, 
consists  virtually  of  a  direct-current  armature  revolving 
in  an  induction  motor  field  structure.  Like  an  ordinary 
induction  motor  there  is  no  electrical  connection  between 
primary  and  secondary.  The  primary  may  be  wound  for 
a  high  line  potential,  while  the  secondary  pressure  may  be 
of  any  value  suitable  for  satisfactory  commutation,  since  it 
is  short  circuited  on  itself  through  the  brushes. 

The  behavior  of  the  repulsion  motor  is  nearly  identical 
with  that  of  the  direct-current  series  motor,  i.e.,  it  shows 
maximum  torque  at  starting,  increase  of  torque  with  in- 
crease of  speed,  with  nearly  constant  efficiency  throughout 
wide  variations  of  speed. 

Load  and  impressed  voltage  limit  the  maximum  speed 


288     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

of  the  motor,  the  maximum  speed,  however,  bearing  no 
relation  to  the  synchronous  speed.  The  motor  circuits 
have  a  comparatively  high  reactance,  so  that  the  power 


Fig.  130.    A  General  Electric  750  H.P.  Induction  Motor 

factor  is  low  on  starting  ;  but  with  the  repulsion  motor  a 
low  power  factor  is  not  associated  with  a  small  torque,  the 
maximum  torque  occurring  simultaneously  with  the  smallest 
power  factor. 

The  power  factor  increases  with  increase  of  load,  and 


MOTORS 


289 


attains  a  fairly  large  value  at  one  third  synchronous  speed. 
Power  factors  of  nearly  90  per  cent  have  been  obtained 
throughout  wide  variations  of  speed. 


PERC 

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CALCULATED  CURVES  OF  175-h.p 
REPULSION    MOTOR,  AT  1500  VOLTS. 

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The  high  power  of  the  repulsion  motor  is  due  to  the 
leading  current,  which  is  generated  by  the  conductors  of 
the  secondary  cutting  the  primary  ftux.  This  leading  cur- 


2QO       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

rent  is,  however,  not  of  sufficient  magnitude  at  practical 
speeds  to  entirely  compensate  for  idle  currents,  but  by  the 
addition  of  an  auxiliary  or  second  circuit  a  compensated 
type  of  motor  is  produced  which  may  be  made  to  give 
unity  power  factor  at  any  load. 

The  efficiency  of  the  repulsion  motor  ranges  from  80  to 
85  per  cent  (including  losses  in  couplings,  or  gearing),  for 
motors  of  from  50  to  200  horse-power. 

Fig.  131  shows  the  calculated  characteristics  of  a  175 
horse-power  single-phase  1,500  volt  repulsion  motor,  pre- 
sented by  Mr.  W.  I.  Slichter  in  a  paper  before  the 
American  Institute  of  Electrical  Engineers.  From  these 
curves  it  can  be  readily  seen  "  that  the  repulsion  motor  is 
well  suited  for  efficient  operation  at  light  loads,  and  pos- 
sesses fairly  good  constants  at  low  speeds." 


BIBLIOGRAPHY 

Elements  of  Electrical  Engineering.  —  Steinmetz.  McGraw  Publishing 
Company.  New  York.  1902. 

Alternating  Currents  and  Alternating  Current  Machinery.  —  Jackson 
&  Jackson.  Macmillan  Co.  New  York.  1901. 

The  Induction  Motor.  —  De  La  Tour-Mailloux.  McGraw  Publishing 
Company.  New  York.  1903. 

Notes  on  the  Theory  of  the  Synchronous  Motor. —  Steinmetz.  Trans- 
actions American  Institute  Electrical  Engineers,  Vol.  19,  p.  781. 

The  Repulsion  Motor.  —  Steinmetz.  Transactions  American  Institute 
Electrical  Engineers,  Vol.  21,  p.  75. 

Speed-Torque  Characteristics  of  the  Single-Phase  Repulsion  Motor. — 
Slichter.  Transactions  American  Institute  Electrical  Engineers,  Vol.  24, 
p.  6. 


CHAPTER   IX 
CONVERTERS 

A  CONVERTER  is  a  transforming  apparatus  consisting  of 
one,  field  winding  and  one  armature,  the  latter  being  con- 
nected to  a  direct-current  commutator  at  one  end  and 
alternating-current  slip  rings  at  the  other  end. 

When  the  machine  is  designed  to  transform  alternating 
into  direct  current  it  is  termed  a  synchronous  converter. 
When  it  is  designed  to  transform  direct  current  into  alter- 
nating current  the  machine  is  termed  an  inverted  converter^ 

In  high-tension  electric  transmission  the  converter  finds 
its  chief  use  in  transforming  alternating  into  direct  cur- 
rent suitable  for  operating  railway  motors,  factory 
motors,  etc. 

If  the  brushes  which  rest  on  the  slip  rings  be  supplied 
with  alternating  current  of  the  proper  pressure,  the  armature 
will  rotate  like  the  armature  of  a  synchronous  motor,  that 
is,  in  synchronism  with  the  E.M.F.  impressed  on  the  cir- 
cuit. When  rotating  in  this  manner,  direct  current  may 
be  taken  from  the  brushes  on  the  commutator. 

The  power  which  is  delivered  to  the  slip  rings  of  a  con- 
verter must  be  sufficient  to  supply  the  direct-current  circuit, 
and  also  overcome  the  losses  due  to  resistance,  inductance, 
hysteresis,  friction,  windage  and  eddy  currents. 

The  armature  winding  of  a  converter  is  of  the  closed- 
coil  type,  and  similar  to  that  of  a  direct-current  dynamo, 
with  the  taps  leading  to  the  slip  rings, 

291 


LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


Each  slip  ring  is  connected  to  the  armature  winding  by 
as  many  taps  as  there  are  pairs  of  poles  on  the  field  magnet, 
these  taps  being  equidistant  from  each  other. 

A  converter  may  be  fitted  with  any  desirable  number  of 
rings.  When  fitted  with  ;/  rings  the  taps  are  distant  from 

each  other  by   -  th  of  the  distance  between  the  centers  of 
n 

two  successive  north  poles  from  each  other. 


Fig.  132.    Section  of  Periphery  of  Commutator  of  Converter 

The  E.M.F.  at  the  several  brushes  of  a  converter  may  be 
found  in  the  following  manner: 

Let  Ed  =  pressure  between  successive  direct-current  brushes. 
En  =  effective  pressure    between    successive    rings    of    an 

«-ring  converter. 

em=  maximum  E.M.F.  in  volts  induced  in  any  given  arma- 
ture conductor.     (This  E.M.F.  is  generated  when 
the  conductor  is  under  the  center  of  a  pole.) 
c  =  the  number  of  armature  conductors  in  a  unit   angle 
(electrical)  of  its  periphery. 


CONVERTERS  293 

The  electrical  angle  subtended  by  the  centers  of  two  suc- 
cessive poles  of  like  polarity  is  equal  to  2?r.  In  the  dia- 
grammatical representation  of  a  section  of  the  periphery  of 
the  commutator,  the  pressure  set  up  in  a  given  conductor 
is  considered  as  varying  as  the  cosine  of  the  angle  of  its 
position  with  respect  to  a  point  directly  under  the  center  of 
a  given  pole,  the  value  of  the  angle  being  taken  in  electrical 
degrees.  Thus  at  a  given  angle  a  in  the  diagram,  Fig.  132, 
the  E.M.F.  produced  in  a  conductor  is  em  cos  a  volts. 

Consider  an  elemental  section  of  the  armature.  In  each 
section  there  are  cda  conductors,  in  each  of  which  is  the 
above  E.M.F.  If  these  conductors  are  connected  in  series 
the  pressure  which  is  generated  is  equal  to  emc  cos  a  da  volts. 

If  the  E.M.F.  between  any  two  successive  direct-cur- 
rent brushes  be  derived  by  integration  and  be  written  equal 
to  this  value  Ed,  the  magnitude  of  em  can  be  determined. 

rts 

Thus,  Ed  =   I       emc  cos  ado.  =  2  emc 

J 


The  electrical  angular  distance  between  the  taps  of  two 

27T 

successive  rings  01  an  n-nng  converter   is  equal  to  -- 

Hence  the  maximum  E.M.F.  is  generated  in  the  windings 
between  the  two  taps  when  the  taps  are  spaced  as  equal 
angular  distances  from  the  center  of  a  pole.  The  value  of 
this  E.M.F.  is  equal  to 


I  —  i 

V2  En  =    I 

J 


emc  cos  eu/a  =  2  tmc  sn  - 

TT  » 

2 


294       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

Hence  the  effective  pressure  between  successive  rings  is 
,5.-^  sin*. 

V2  « 

To  ascertain  the  maximum  value  of  the  alternating  current 
supplied  to  a  converter,  assume  that  after  deducting  the 
losses  therein  the  power  intake  in  alternating  current 
equals  the  direct -current  output.  Disregard  the  losses 
for  the  moment,  and  let  En  represent  the  voltage  and  /„ 
represent  the  alternating  current  in  the  armature  windings 
between  successive  slip  rings.  Then  for  the  sections  of 
the  armature  periphery  covered  by  each  pair  of  poles, 

Edld  =  nEJn 

where  Ed  represents  the  quantity  assigned  to  it  above,  and 
Id  is  the  current  between  successive  direct-current  brushes. 
Hence,  the  maximum  value  of  the  alternating  current  is 


TT 

n  sin  - 
n 


Ratios  of  Conversion  and  Capacity.  —  The  effective 
pressure  between  the  successive  rings  of  a  converter  is,  as 
has  been  shown,  equal  to 


If  the  numerical  values  representing  converters  with 
different  numbers  of  rings  be  substituted  in  the  equation, 
it  is  found  that  the  coefficients  by  which  the  pressure  be, 
tween  direct-current  brushes  must  be  multiplied  in  order 


CONVERTERS  295 

to  ascertain  the  effective  pressure  between  successive  rings 
is  as  follows : 

For  two-ring  converters      .  .  .  0.707 

For  three-ring  converters  .  .  .  0.612 

For  four-ring  converters     .  .  .  0.500 

For  six-ring  converters       .  .  .  0.354 

Owing  to  the  non-sinusoidal  distribution  of  flux  in  the 
air-gap  of  commercial  converters,  however,  these  coefficients 
are  only  approximate. 

Converters  of  the  synchronous  type  with  closed-coil 
windings  on  the  armature  have  the  following  relative 
capacities  :  as  a 

CAPACITY 

Direct-current  generator    .     .     .  100 
Single-phase  converter       ...       85 

Three-phase  converter       .     .     .  134 

Four-phase  converter         .     .     .  164 

Six-phase  converter       ....  196 

Twelve-phase  converter      .     .     .  227 

Modern  converters  can  stand  overloads  which  are  only 
limited  by  satisfactory  commutation. 

Methods  of  Starting  Converters.  —  Since  the  synchronous 
converter  is  a  synchronous  motor  it  usually  requires  some 
device  to  bring  it  up  to  speed.  The  three  most  impor- 
tant methods  used  in  practice  to  start  up  a  converter  are : 

(1)  The  machine  may  be  directly  connected  to  the  supply 
circuit    through     auto-transformers    or   impedance     coils. 

(2)  By  means  of  a  small  induction  motor.      (3)   Starting 
the  converter  as  a   shunt-wound    motor  from  the  direct- 
current  end. 


296     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

(1)  If  an  impedance  coil  is  used  it  is  placed  between 
the  line  and  the  armature  of  the  converter,  its  function  be- 
ing to  keep  down  the  pressure  and  thus  obviate  the  exces- 
sive   rush    of    current  and  consequent    line    disturbances 
which  would  otherwise  occur  were  the  rated  voltage  im- 
pressed directly  upon  the  armature  when  at  a  standstill. 
In  some  instances  taps  are  led  out  from  the  windings  and 
the  coil  is  gradually  cut  out  as  the  armature  speeds  up,  so 
that  when  synchronism  is  attained  the  coil  is  completely 
short  circuited.     This  method  of  starting  may  be  more  or 
less    objectionable,    owing  to   the   reaction   which   follows 
upon   the  transmission  line.      Owing  to  the  fact  that  the 
starting  current  is  considerably  greater  than  the  full-load 
running  current,   and  the  power  factor  low,  there  is  but 
small  energy  consumption  ;  hence  the  line  disturbances  may 
be  undesirable. 

If  an  auto-transformer  is  used  for  starting  instead  of  the 
impedance  coil,  it  is  connected  in  parallel  with  the  line  in- 
stead of  in  series  with  it.  A  number  of  taps  are  led  out 
from  various  parts  of  the  auto-transformer  winding  to  a 
central  point,  so  that  the  impressed  voltage  on  the  con- 
verter can  be  regulated  as  desired.  By  means  of  this  con- 
troller the  pressure  is  gradually  raised  as  the  machine  comes 
up  to  speed.  When  synchronous  speed  is  attained  the 
rated  voltage  is  impressed  on  the  machine's  terminals. 
Starting  a  converter  through  an  auto-transformer  generally 
causes  less  disturbance  on  the  line  than  the  use  of  an  im- 
pedance coil.  This  is  due  to  the  fact  that  the  auto-trans- 
former limits  the  starting  current  on  the  line  in  proportion 
as  the  impressed  voltage  is  less  than  that  on  the  line. 

(2)  Starting  a  converter  by  means  of  an  induction  motor 
In  this  method  of  starting,  a  small  induction  motor  with  a 


CONVERTERS 

synchronous  speed  higher  than  that  of  the  converter  is 
mounted  on  one  end  of  the  converter's  shaft.  To  start  the 
converter  the  motor  is  connected  across  the  secondaries  of 
the  transformer.  The  converter  then  gradually  comes  up 
to  speed,  after  which  the  induction  motor  is  disconnected 
and  rims  normally  without  load. 

(3)  Starting  the  converter  as  a  direct-current  shunt 
motor  from  the  direct-current  end  is  by  far  the  most  satis- 
factory method,  as  no  line  disturbances  occur.  In  this  case 
a  starting  resistance  or  external  rheostat  must  be  provided. 
The  machine  is  gradually  brought  up  slightly  above  syn- 
chronous speed  by  cutting  out  resistance,  exactly  as  a 
direct-current  shunt  motor  is  started.  The  starting  motor 
is  then  cut  out  and  its  field  circuit  opened  ;  after  which  the 
converter  may  be  connected  to  the  alternating-current 
mains,  the  armature  quickly  falling  into  synchronism.  In 
cases  where  several  converters  are  installed  in  a  sub-station, 
a  small  motor-generator  is  sometimes  employed  to  obtain 
direct  current  for  starting. 

The  apparent  power  of  a  converter  at  starting  is  approx- 
imately that  which  is  indicated  by  the  volt-ampere  input, 
for  converters  with  either  solid  or  laminated  poles.  But  in 
a  converter  with  laminated  poles  the  current  is  more  nearly 
in  phase  with  the  E.M.F.  on  account  of  the  magnetizing 
current  necessary  to  set  up  the  field  flux  being  smaller  be- 
cause of  the  subdivided  iron.  By  subdividing  the  iron  the 
induction  can  penetrate  farther  into  the  poles. 

Troubles  of  Converters.  — Hunting  of  Converters  on  High- 
Frequency  Circuits.  —  The  converter  being  a  synchronous 
apparatus  is  subject  to  all  the  troubles  of  a  synchronous 
motor.  But  since  no  mechanical  power  is  taken  off,  a  con- 
verter is  much  more  sensitive  than  a  synchronous  motor  to 


298     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

slight  variations  in  the  supply  of  electrical  energy.  The 
most  frequent  source  of  trouble  with  a  converter  is  a  ten- 
dency to  hunt  or  pump.  This  phenomenon,  which  is  both 
a  mechanical  and  electrical  oscillation,  is  due  to  a  variety 
of  causes  :  (i)  Slight  variations  in  the  angular  velocity  of 
the  prime  mover.  (2)  Slight  variations  in  the  voltage  im- 
pressed on  the  converter.  (3)  Absence  of  sufficient  arma- 
ture reaction.  (4)  Sudden  changes  of  speed  in  the  prime 
mover.  (5)  Sudden  change  of  load. 

(i)  Variations  in  the  angular  velocity  of  the  prime  mover 
are  mainly  due  to  faults  of  design.  If  the  prime  mover  is 
a  steam  engine,  the  connecting  rod  may  be  too  short,  the 
governor  be  over-sensitive,  or  the  flywheel  may  possess  in- 
sufficient capacity.  An  increasing  angular  velocity  results 
in  a  slight  increase  in  the  frequency  of  the  supply  circuit. 
Hence,  the  current  of  the  converter  increases,  and  the  arma- 
ture tending  to  come  in  a  more  favorable  position  with  re- 
spect to  the  field,  a  powerful  force  is  exerted  to  increase  the 
speed  of  the  converter.  But  the  armature  of  the  converter 
by  reason  of  its  weight  possesses  considerable  inertia,  and 
a  certain  time  interval  is  necessary  to  effect  a  change  in  its 
position.  Hence  there  is  liability  of  the  synchronizing  im- 
pulse being  oversufficient  to  bring  the  armature  to  the  fre- 
quency which  existed  at  the  time  of  the  impulse,  so  that  the 
armature  will  be  speeded  up  above  synchronism. 

When  the  converter  armature  speeds  up,  the  prime  mover 
may  be  approaching  a  part  of  its  cycle  where  the  angular 
velocity,  and  likewise  the  frequency  of  current,  are  de- 
creasing, so  that  the  tendency  is  to  speed  the  converter  ar- 
mature above  synchronism,  and  so  throw  it  out  of  step.  The 
action  of  the  prime  mover  in  the  opposite  direction,  or  the 
other  half  of  its  cycle,  is  the  same. .  Thus  the  converter  is 


CONVERTERS  299 

continually  oscillating  either  above  or  below  its  proper 
phase  position,  and  likewise  its  instantaneous  speed  is  re- 
peatedly oscillating  above  or  below  synchronous  speed. 
Such  pumping  or  hunting  action  may  also  cause  seri- 
ous disturbance  to  other  synchronous  machinery  in 
circuit. 

With  water  wheels  the  angular  velocity  throughout  a 
cycle  is  constant,  and  hunting  from  this  cause  is  of  rare 
occurrence. 

(2)  Hunting  caused  by  variations  of  impressed  voltage. 
Changes  of  impressed  voltage  may  result  from  over-high 
line   constants,   such  as    inductance    or   resistance.     If  a 
sudden  change  of  mechanical  load  comes  on  the  converter, 
a  drop  in  its  impressed  voltage  may  occur  due  to  high  line 
inductance  or  resistance.     But    since    both   the  magnetic 
circuit  and  the  armature  possess  more  or  less  inertia,  an 
instantaneous  change  to  a    new    condition  cannot    occur. 
Before  a  response  to  altered  conditions  can  take  place,  the 
counter  E.M.F.  may  attain  a  value  high  enough  to  exert 
a  pull  on  the  armature  sufficient  to  alter  the  phase  rela- 
tions of  current  and  E.M.F.     Thus  an  impulse  is  given  to 
the  converter  armature  to  fall   out  of  step,  and  hunting 
ensues. 

(3)  Hunting  caused  by  absence  of  armature  reaction. 
Lack  of  armature  reaction  in  a  converter  is  the  result  of 
an    equilibrium  between  two    equal    and    opposite   forces. 
Since  the  brushes  on  the  commutator  are  set  at  the  neu- 
tral position,  the   action   of    the  direct   current   causes  a 
distortion  of  the  field  flux  in  the  direction  of  rotation.     The 
effect  of  the  alternating  current  (with  unity  power  factor) 
causes  an   equal  reaction  which  is   opposite    in  direction. 
When  a  change  occurs  in  the  values  of  either  or  both  of 


300      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

these  reactions  due  to  a  drop  in  power  factor,  the  mag- 
netizing or  wattless  component  of  alternating  currents  ex- 
erts a  demagnetizing  action  on  the  field,  and  thus  instable 
operation  of  the  converter  may  occur. 

The  effect  of  a  sudden  change  of  load  or  speed  is  to 
cause  a  displacement  in  the  phase  relations  of  current  and 
E.M.F.  in  a  manner  similar  to  a  synchronous  motor.  In- 
ertia of  the  revolving  element  prevents  its  instantaneous 
response  to  the  new  conditions.  When  it  does  respond 
the  new  value  is  exceeded,  and  oscillation  on  both  sides  of 
a  mean  value  occurs. 

Racing  of  the  armature  is  a  common  cause  of  trouble 
with  inverted  converters.  If  from  any  cause  the  current 
of  an  inverted  converter  lags  behind  its  E.M.F.,  the  ten- 
dency of  the  lagging  current  is  to  demagnetize  the  field. 
The  armature  then  begins  to  race  in  a  manner  similar  to 
an  unloaded  shunt  motor  with  weakened  fields. 

Converters  operate  most  successfully  on  25  to  40  cycles, 
although  there  are  a  number  of  Western  transmission 
companies  that  operate  converters  on  60  cycle  circuits, 
and  with  perfect  satisfaction.  A  60  cycle  converter  is, 
however,  a  very  sensitive  element  on  the  line,  and  evinces 
a  decided  tendency  to  hunting.  Moreover,  a  converter 
designed  for  use  on  a  60  cycle  circuit  must  either  be  run 
at  a  very  high  speed,  or  else  have  a  large  number  of  poles 
with  brushes  set  close  together.  If  run  at  a  high  speed 
the  brush  and  commutator  wear  is  quite  appreciable,  and 
the  humming  noise  is  very  objectionable.  If  the  machine 
is  built  with  a  large  number  of  poles  the  brushes  must  be 
set  close  together  to  be  conveniently  handled,  and  there 
is  danger  of  flashing  or  sparking  over  from  one  brush  to 
the  other  on  the  surface  of  the  commutator. 


CONVERTERS  301 

Types  of  American  Converters.  —  Fig.  133  shows  a  750 
kilowatt,  six-phase,  General  Electric  converter.  The  field- 
magnet  yoke  is  made  of  cast  iron,  the  upper  half  being 
fastened  to  the  lower  by  bolts  located  in  recesses  in  the 
sides  of  the  frame.  The  object  of  this  method  of  fasten- 
ing is  to  avoid  the  unsightly  appearance  of  external  bolts. 


Fig.  133.    A  750  Kilowatt  Six-Phase  Converter 


The  poles  are  constructed  of  solid  steel  castings  and  are 
bolted  to  the  frame  to  permit  of  easy  removal  for  repairs. 
The  lower  half  of  the  frame  is  made  separate  from  the 
bed  plate,  which  permits  the  entire  frame  to  be  slid  along 
the  bed  plate  parallel  to  the  shaft,  in  case  access  must  be 
had  to  the  armature. 


3O2      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  armature  is  bar  wound,  the  upper  bars  being  con- 
nected to  the  lower  bars  by  means  of  soldered  clips  on 
the  collector  side  of  the  armature. 

The  collector  rings  are  separated  by  air  spaces  to  afford 
sufficient  insulation  and  freedom  from  short  circuits.  The 
brushes  on  the  collector  rings  are  made  of  copper  leaf, 
while  those  on  the  commutator  are  made  of  carbon  and 
are  held  in  shank  brush  holders. 

In  order  to  insure  cool  running,  the  spokes  of  the  arma- 
ture spider  are  fitted  with  small  vanes  which  produce  enough 
centrifugal  action  to  force  an  air  current  between  the  laminae 
of  the  armature,  over  its  windings  and  around  the  poles. 

An  automatic  oscillator  or  end-play  device  is  used  on 
the  shaft  to  give  the  armature  an  occasional  to  and  fro 
motion  parallel  to  the  shaft,  and  thus  give  uniform  wear  on 
commutator  and  collectors. 

Fig.  134  shows  a  1,500  kilowatt,  three-phase,  Westing- 
house  converter,  which  is  the  largest  converter  so  far 
constructed. 

The  armature  is  wound  like  an  ordinary  direct-current 
generator  of  large  output,  the  windings  being  cross- 
connected  so  as  to  facilitate  commutation.  At  regular 
points  around  the  periphery  of  the  armature,  taps  are  led 
out  to  the  collector  rings  on  the  left  side  of  the  armature. 

The  field  of  the  machine  is  wound  with  copper  strap  in 
a  manner  similar  to  a  large  direct-current  generator,  and 
is  compounded  to  compensate  for  line  losses. 

Motor-Generators  versus  Converters. —  The  converter  as 
a  translating  apparatus  possesses  the  advantage  of  higher 
efficiency,  since  there  is  but  one  machine  instead  of  two ; 
consequently  machine  losses  are  smaller.  Likewise  its 
cost  is  lower,  as  but  one  machine  is  needed. 


CONVERTERS 


303 


304      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

A  converter  may  be  compounded  to  compensate  for  the 
voltage  drop  which  occurs  in  the  generator  and  transmis- 
sion circuit ;  hence  it  exercises  no  objectionable  influence 
upon  the  voltage  of  the  transmission  system. 

On  the  other  hand,  the  voltage  which  is  taken  off  at  the 
direct-current  end  bears  a  fixed  relation  to  the  pressure  of 
the  received  E.M.F.  However,  by  maintaining  the  E.M.F. 
of  supply  reasonably  constant,  it  is  possible  by  means  of 
regulating  devices  or  compounding,  so  to  adjust  and  control 
the  E.M.F.  delivered  by  a  converter  that  the  relation  be- 
tween the  pressure  of  supply  and  delivery  will  be  close 
enough  to  be  regarded  as  negligible.  Converters  are  also 
about  20  per  cent  cheaper  than  motor-generators  and  from 
2  to  8  per  cent  more  economical  of  power. 

On  low-frequency  circuits  the  operation  and  behavior  of 
converters  are  eminently  satisfactory,  and  they  require  but 
little  attention.  But  on  transmission  lines  operating  at  60 
cycles  or  above,  the  untrustworthy  behavior  of  converters 
has  led  many  Western  transmission  companies  to  adopt 
motor-generators  as  translating  devices. 

A  motor-generator  consists  of  a  motor,  which  may  be 
either  of  the  synchronous  or  induction  type,  directly 
coupled  to  a  direct-current  generator. 

The  salient  points  of  advantage  which  a  motor-generator 
possesses  over  a  converter  are  :  ( i )  The  E.M.F.  of  delivery 
is  independent  of  the  E.M.F.  of  supply  and  may  be  adjusted 
over  a  wide  range  to  suit  any  conditions  for  which  direct 
current  may  be  employed.  (2)  A  motor-generator  may  be 
used  without  putting  in  a  step-down  transformer,  whereas 
with  a  converter  the  transformer  is  generally  required.  (3) 
If  an  induction  motor  is  used  to  drive  the  generator,  peri- 
odic fluctuations  in  the  speed  of  the  central  station  gen- 


CONVERTERS 


305 


erator  will  not  affect  the  satisfactory  operation  of  the 
machines.  In  other  words,  hunting  or  pumping  is  unknown 
when  an  (induction)  motor-generator  is  used  as  the  trans- 
lating apparatus.  Moreover,  momentary  interruption  of 
the  supplying  current  or  a  sudden  overload  on  the  induction 
motor  may  give  rise  to  little  if  any  disturbance,  whereas 
with  a  converter  serious  hunting  may  occur. 

(4)  No  highly  skilled  attendants  are  required  when  motor- 
generators  are  employed. 

In  American  long-distance  power  transmission  practice, 
the  proportion  of  converters  used  as  translating  apparatus 
is  far  in  excess  of  motor-generators,  which  may  be  consid- 
ered as  indicative  of  the  high  state  of  development  which 
the  converter  has  attained  in  this  country.  In  Europe  the 
reverse  holds  true. 

Efficiencies  of  Motor- Generator  Sets.  —  The  following 
table  shows  the  efficiencies  of  motor-generator  sets  of 
various  outputs,  and  at  different  loads. 

Motor -Generator  Sets —  Combined  Efficiency. 


Quarter 
Load 

Half 
Load 

Three 
Quarter 
Load 

Full 
Load 

One 
and  a 
Quarter 
Load 

One  and 
a  Half 
Load 

400  kw.,  375  revolutions      .     . 

70 

8l 

85.5 

88. 

89.2 

90 

500  kw.,  450  revolutions      .     . 

72 

83 

87 

89. 

90 

91 

800  kw.,  450  revolutions      .     . 

73 

83.5 

87.5 

89-5 

90.2 

91 

1  200  kw.,  450  revolutions      .     . 

77 

86 

89.5 

91. 

91.8 

92 

The  figures  given  apply  to  Bullock  machines.  The 
efficiencies  of  motor-generator  sets  of  other  representative 
manufacturers  will  not  differ  appreciably  from  these  figures. 


306     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 


The  following  tables  are  a  comparison  between  the  rela- 
tive efficiencies  of  static  transformers  and  converters  as 
against  motor-generators.  The  figures  apply  to  200  kilo- 
watt units  in  operation  at  a  sub-station  of  the  Buffalo 
(N.  Y.)  Edison  Company. 


Trans- 
former 

Con- 
verter 

Motor 

Genera- 
tor 

Combined 
Efficiency 

Full  load     

07.  C 

Q^.O 

nc 

92 

87.4 

Three  quarter  load  .     .     . 

97.1 

92.5 

94 

91 

85.54 

One  half  load  

Q6.O 

QO  O 

02 

88  c' 

8l  42 

Comparison  between  the  Net  Efficiencies  of  200  Jfilowatt   Units. 


Motor- 
Generator 

Transformers 
and  Converters 

Difference 

Full  load      

87.40 

8q  47 

2  47 

Three  quarter  load    .... 

85.54 

88.70 

3-16 

One  half  load  

81.42 

84.00 

3.48 

Frequency  Converters.  —  A  frequency  converter  is  an 
apparatus  for  changing  an  alternating  current  of  one  fre- 
quency into  an  alternating-current  of  another  frequency, 
which  may  be  either  higher  or  lower  than  the  received  fre- 
quency. Its  principal  use  is  to  transform  low  frequencies 
into  higher  ones. 

A  frequency  converter  is  essentially  an  induction  motor, 
and  operates  on  the  principle  of  the  variation,  with  slip,  of 
the  frequency  of  its  rotor  E.M.F. 

The  usual  method  for  raising  the  frequency  of  supply  is 
to  couple  a  synchronous  motor  to  the  shaft  of  an  induction 


CONVERTERS 


307 


308       LONG-DISTANCE  ELECTRIC   POWER  TRANSMISSION 

motor,  and  cause  the  driving  motor  to  turn  the  rotor  of  the 
induction  motor  in  an  opposite  direction  to  the  direction  of 
rotation  of  the  driven  motor's  field.  The  primary  windings 
of  the  induction  motor  and  also  the  terminals  of  the  driving 
motor  are  connected  to  the  low-frequency  source  of  supply. 
The  higher-frequency  current  is  taken  from  the  secondary 


Fig.  136.     A  Large-Frequency  Converter  Unit  i 

of  the  induction  motor  by  means  of  slip  rings  mounted  on 
the  shaft. 

The  voltage  of  the  delivered  current  and  its  frequency 
are  governed  by  the  speed  of  the  rotor.  For  definite 
values,  they  are  the  algebraic  sum  of  the  current  variations 
in  both  machines.  When  the  rotor  is  revolved  at  its  rated 
speed  in  a  direction  opposite  to  its  normal  direction  of  rota- 


CONVERTERS  309 

tion,  the  frequency  of  the  delivered  current  is  double  that 
of  the  received  current.  Likewise,  if  the  rotor  is  revolved 
at  half  speed  in  its  normal  direction,  the  frequency  of  the 
output  is  one  half  that  of  the  supply.  The  output  of  the 
synchronous  motor  which  drives  the  frequency  converter 
must  be  of  the  same  proportion  of  the  total  output  as  the 
increase  in  frequency  is  to  the  higher  frequency. 

Use  of  Frequency  Converters  in  High-Tension  Practice.  — 
In  addition  to  transforming  low-frequency  current  into 
frequencies  suitable  for  the  operation  of  lights  and  other 
apparatus  which  require  high  frequencies  for  satisfactory 
operation,  or  vice  versa,  frequency  converters  find  a  valuable 
field  of  service  in  cases  where  several  transmission  lines 
operated  at  different  frequencies  supply  a  center  of  distri- 
bution. In  such  cases,  the  frequency  converter  is  an  alter- 
nating-current generator  driven  by  an  induction  or  syn- 
chronous motor. 

A  notable  instance  of  this  kind  is  that  of  the  electrical 
supply  of  Montreal,  Canada.  Energy  is  supplied  by  three 
transmission  companies,  all  operating  at  different  frequen- 
cies. The  three  frequencies,  66,  60,  and  30  cycles  respec- 
tively, are  transformed  by  five  frequency  converter  units 
into  63  cycle  current  which  is  supplied  to  all  customers  in 
the  city.  Fig.  1 36  shows  a  type  of  large-frequency  con- 
verter unit. 


310      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

BIBLIOGRAPHY 

Elements  of  Electrical  Engineering.  —  Steinmetz.  McGraw  Publishing 
Co.  N.  Y.  1902. 

Alternating  Currents  and  Alternating  Current  Machinery.  —  Jackson 
&  Jackson.  Macmillan  Co.  N.  Y.  1901. 

The  Rotary  Converter.  —  Berg.  Transactions  American  Institute  of 
Electrical  Engineers,  Vol.  18,  p.  607. 

The  Design  and  Action  of  the  Rotary  Converter.  —  Rushmore. 
(Serial.)  Engineering  Magazine,  N.  Y.,  Vol.  22  (1901).  PP-  4*4-422, 


Energy  Transformations  in  the  Synchronous  Converter.  —  Franklin. 
Transactions  American  Institute  Electrical  Engineers,  Vol.  20,  p.  876. 

Operation  of  Converters.  —  American  Electrician,  N.  Y.,  Sept.,  1903. 

Voltage  Regulation  of  Rotary  Converters.  —  Lincoln.  Electric  Club 
Journal,  Pittsburg,  March,  1904,  p.  55. 


CHAPTER    X 
PRACTICAL    PLANTS 

Architectural  Designs  of  Buildings  for  Hydro-Electric 
Central  Stations.  —  The  majority  of  power  houses  gener- 
ating current  for  long-distance  transmission  are  similar 
in  architectural  features,  differing  chiefly  in  dimensions, 
minor  details,  and  materials  of  construction.  The  type  of 
building  which  has  now  become  almost  the  standard  de- 
sign as  a  containing  structure  for  hydro-electric  machinery 
is  a  square  or  rectangular  building  with  its  greatest 
dimension  longitudinally. 

Foundations  for  power  houses  are  usually  concrete  and 
granite  masonry.  In  a  few  instances  wooden  piles  have 
been  used  where  the  character  of  the  soil  did  not  permit 
the  use  of  a  masonry  foundation.  The  foundation  of  the 
Sault  Ste.  Marie  structure,  which  is  the  largest  building 
thus  far  erected  for  housing  hydro-electric  machinery,  has 
a  wooden  pile  support. 

Various  materials  of  construction  are  employed  for 
power-house  structures,  among  which  may  be  included 
nearly  all  of  the  common  building  materials,  such  as  wood, 
brick,  concrete,  granite  masonry,  sandstone,  corrugated 
iron,  and  structural  steel.  Except  for  power  houses  of 
small  output,  wood  is  now  rarely  used  entirely  as  a  build- 
ing material. 

The  three  materials  most  employed  for  this  purpose  are 
concrete,  brick,  and  granite  masonry,  with  or  without 


312     LONG-DISTANCE    ELECTRIC    POWER  TRANSMISSION 

structural  steel  frames.  Some  buildings  on  the  Pacific 
coast  are  constructed  of  corrugated  iron  over  a  wooden 
frame,  while  in  a  few  instances  (notably  the  Sault  Ste. 
Marie  Plant)  power  houses  have  been  constructed  of  the 
sandstone  which  was  excavated  from  the  canal. 

Floors  for  hydro-electric  stations  are  made  of  concrete, 
cement,  brick,  tile  over  concrete,  and,  in  a  few  instances, 
wood.  When  the  structure  is  provided  with  a  gallery,  it 
is  constructed  either  of  wood  (rarely)  or  of  steel  and  con- 
crete ;  not  infrequently  it  is  constructed  of  a  combination 
of  the  three  materials. 

Roof  trusses  are  usually  of  the  arched  type  and  are 
generally  made  of  structural  steel  in  a  variety  of  designs. 

Roof  coverings  consist  of  corrugated  iron,  a  combina- 
tion of  concrete  tar  and  gravel,  or  asbestos  covered  by  one 
of  the  numerous  patented  roof  coverings. 

The  general  practice  with  most  transmission  companies 
is  to  erect  as  substantial  and  fire  proof  structures  as  pos- 
sible, since  the  ultimate  economy  and  safety  are  far  greater. 

Arrangement  of  Machinery  and  Apparatus  in  High- 
Tension  Central  Stations.  —  In  the  arrangement  and 
location  of  hydraulic  and  electrical  machinery  and  auxiliary 
apparatus  in  high-tension  plants  the  controlling  factors  are 
considerations  of  safety,  space  economy,  and  accessibility, 
and  in  many  instances  the  necessity  of  conforming  strictly 
with  the  peculiar  circumstances  of  the  case. 

In  most  Western  practice,  where  the  water  supply  is 
conducted  through  the  power  plant  latitudinally,  the 
hydraulic  machines  are  installed  with  their  shafts  parallel 
to  the  walls  of  the  structure,  or  lengthwise  in  the  building 
and  close  to  the  wall.  In  cases  where  the  water  is  con- 
ducted through  the  structure  longitudinally  the  hydraulic 


PRACTICAL    PLANTS  313 

machines  are  usually  set  with  shafts  parallel  to  the  width 
of  the  building. 

When  vertical  turbines  are  used  the  hydraulic  units  are 
usually  installed  in  a  straight  line  a  few  feet  from  the 
lengthwise  wall  of  the  building. 

In  some  hydro-electric  power  houses,  notably  those  in 
the  East,  the  building  is  divided  into  compartments  by 
partitions,  the  turbines  being  installed  in  a  separate  wheel 
room,  and  the  generators  in  so-called  generator  chambers. 
The  wheel  chambers  generally  have  arched  concrete  roofs 
with  concrete  floors  ana  sides,  while  the  head  wall. that 
separates  each  chamber  from  the  generator  room  is  5  or  6 
feet  thick,  and  is  fitted  with  a  large  bulkhead  of  cast  iron, 
which  carries  a  water-tight  bearing  for  the  wheel  shaft. 

In  the  location  of  transformers  practice  varies  widely. 
They  are  either  installed  in  the  power  plant  proper  on  the 
main  floor  near  the  walls,  or  in  line  with  the  space  back  of 
the  low-tension  switchboard  on  one  side  and  the  exciters  on 
the  other,  or  are  placed  in  a  compartment  partitioned  off 
from  the  rest  of  the  structure,  or  are  located  on  the  upper  or 
gallery  floor.  In  some  plants  they  are  placed  in  a  separate 
transformer  house.  In  plants  where  air-blast  transformers 
are  used  they  are  placed  on  the  main  floor  with  air  cham- 
bers underneath  or  in  a  basement. 

Switchboards  in  hydro-electric  plants  are  installed  either 
on  the  same  floor  as  the  generators,  on  the  side  of  the  power 
house  or  at  the  end,  or  are  mounted  on  a  platform  or  ros- 
trum of  masonry  a  few  feet  above  the  floor  level,  or  they 
are  installed  in  a  gallery  above  the  main  floor.  The  atter 
practice  is  more  general  in  cases  of  plants  of  large  output  at 
very  high  potentials. 

As  in  the  case  of  transformers,  no  uniformity  of  practice 


314     LONG-DISTANCE   ELECTRIC    POWER   TRANSMISSION 

obtains  in  the  location  of  switchboards.  In  many  instances, 
the  matter  of  convenience,  accessibility,  and  economy  de- 
mands that  the  switchboard  be  installed  on  the  same  floor 
as  the  generators,  so  that  the  men  attending  wheels  and 
generators  can  also  perform  the  switching  operations. 

In  some  high-tension  plants  on  the  Pacific  coast,  the 
high-potential  board  is  installed  separately  from  the  gener- 
ator switchboards,  being  usually  mounted  in  a  gallery  over 
and  slightly  to  the  rear  of  the  generator  board,  and  is 
placed  half  way  between  the  inner  rail  of  the  crane  and  the 
wall  of  the  building,  and  facing  the  tailrace. 

The  lightning  arresters  for  high-tension  stations  are  in- 
stalled either  in  a  separate  building,  termed  the  lightning  ar- 
rester house,  or  are  located  in  the  main  building.  Arresters 
for  protecting  transformers  are  mounted  on  the  faces  of 
vertical  marble  panels  located  near  the  transformers. 

Parallel  Operation  of  Plants.  —  Many  Western  long- 
distance transmission  plants  miles  apart  are  successfully 
operated  in  parallel,  the  problem  of  parallel  running  being 
regarded  as  no  more  serious  than  the  parallel  operation  of 
direct-current  plants.  A  notable  instance  is  the  system 
of  the  Edison  Electric  Company  of  California,  which  con- 
sists of  seven  plants  separated  by  wide  distances,  all  of 
which  are  operated  in  parallel  with  the  greatest  of  ease. 

Regulation  of  Plants.  —  In  long-distance  power  plants 
one  of  the  highest  essentials  of  successful  operation  is  good 
regulation.  The  requirements  of  close  regulation  are  in 
the  main  a  recapitulation  of  the  principles  outlined  in  pre- 
vious chapters.  They  are:  (i)  A  considerable  voltage  vari- 
ation in  the  generators,  and  generators  and  transformers 
designed  for  close  inductive  load  regulation ;  (2)  a  trans- 
mission line  so  designed  that  the  capacity  current  will  be 


PRACTICAL   PLANTS  315 

a  minimum ;  (3)  avoidance  of  attempts  to  balance  the 
capacity  of  the  circuits  against  the  power  lag  ;  (4)  constant 
capacity  of  the  line  balanced  with  reactance;  (5)  the 
variable  inductance  of  circuits  and  the  induction  motor 
load  to  be  balanced  by  variable  capacity  in  the  form  of 
synchronous  motors. 

Sub-Stations:  Materials  of  Construction  and  Arrange- 
ment of  Apparatus.  —  Architecturally  the  majority  of  high- 
tension  sub-stations  are  closely  similar  to  the  main  power 
structures.  The  type  of  building  generally  used  is  of 
square  or  rectangular  shape,  one  or  two  stories  in  height, 
depending  on  the  capacity  in  translating  apparatus  which 
is  needed  at  the  particular  point  of  distribution.  In  West- 
ern practice  sub-stations  are  sometimes  designed  so  that  a 
second  story  may  be  added  to  provide  for  increased  de- 
mands for  power. 

Considerations  of  safety  and  reliability  of  operation  de- 
mand that  sub-stations  be  of  the  most  substantial  and  fire- 
proof character.  Formerly  it  was  the  practice  to  place  the 
translating  apparatus  in  a  hastily  put  up  structure,  often- 
times of  a  character  which  barely  protected  the  machinery 
from  the  elements.  In  the  best  modern  practice  as  much 
attention  is  given  to  the  sub-stations  as  to  the  central 
station,  and  their  construction  is  of  a  very  rugged  character. 
Brick  is  mostly  employed  for  constructing  sub-stations, 
although  stations  of  granite  masonry,  concrete  masonry, 
and  sandstone  are  frequently  met  with  in  Western  practice. 

The  incoming  high-tension  wires  are  passed  into  sub- 
stations through  long  porcelain  sleeves  or  through  marble 
and  glass  bushings ;  and  the  current  is  usually  conducted 
through  a  set  of  single-throw  fused  switches,  one  switch 
per  leg.  Thence  the  high-tension  current  is  passed  through 


316    LONG-DISTANCE    ELECTRIC    POWER    TRANSMISSION 

non-arcing  lightning  arresters  fitted  sometimes  with  static 
interrupters,  finally  being  conducted  to  the  step-down  trans- 
formers. 

Step-down  transformers  in  sub-stations  are  usually 
arranged  in  pairs  or  groups  and  installed  near  the  length- 
wise wall  of  the  building ;  or,  in  case  they  are  the  only 
translating  apparatus  in  the  station,  are  placed  near  the 
center  of  the  structure. 

Switchboards  in  sub-stations  are  generally  installed  near 
the  lengthwise  wall  of  the  structure.  In  most  cases  they 
contain  a  separate  panel  for  each  transformer  and  are 
equipped  with  the  necessary  measuring  and  indicating 
instruments  and  the  protective  devices  which  have  been 
mentioned  before  (Chapter  IV). 

The  switchboard  in  most  sub-stations  is  equipped  with  a 
high-tension  plug  board  which  permits  of  any  desirable 
combination  of  the  incoming  and  outgoing  circuits.  Thus 
in  some  cases  all  of  the  load  may  be  put  on  either,  trans- 
mission line,  or  it  may  be  divided  so  that  the  steady  load  is 
on  one  circuit  and  the  fluctuating  load  on  the  other ;  or 
both  circuits  may  be  connected  in  multiple. 

Cost  of  Electrical  Power  Transmission.  —  To  justify  an 
electrical  transmission  project,  the  value  of  the  energy  at 
the  point  of  distribution  should  at  least  equal  the  value  of 
the  generating  plant  plus  the  cost  of  transmission.  The 
cost  of  energy  at  the  generating  end  being  known  and  its 
value  at  the  receiving  end,  the  difference  between  the 
two  represents  the  maximum  cost  at  which  the  transmis- 
sion will  pay. 

The  factors  which  enter  into  the  cost  of  a  power  trans- 
mission scheme  are :  (£-C&st-  of  water  rights,  the  land 
flooded  by  back-water  or  for  a  reservoir  site ;  (2)  cost  of 


PRACTICAL   PLANTS  3  I/ 

dam  and  its  auxiliaries  which  may  be  conveniently  termed 
the  "hydraulic  end";  (3)  cost  of  powerhouse  and  aux- 
iliary structures  ;  (4)  cost  of  station  machinery  and  auxiliary 
apparatus;  (5)  cost  of  transmission  lines  and  translating 
apparatus ;  (6)  cost  of  operation ;  (7)  cost  of  repairs, 
maintenance,  and  depreciation. 

In  most  instances  there  is  the  additional  cost  of  the 
water-conveying  system,  a  pipe,  flume,  or  canal  line.  The 
cost  of  hydraulic  pipe  differs  widely.  The  table  on  page  60 
may  be  taken  as  a  good  average  of  the  cost  per  foot  of 
riveted  sheet  steel  pipe. 

The  cost  of  buildings  will  include  the  cost  of  the  main 
power  plant  and  auxiliary  houses,  such  as  lightning  arrester 
and  transformer  buildings  (if  such  apparatus  is  not  installed 
in  the  central  station).  Also  the  cost  of  various  sub-stations 
for  distributing  the  power.  Many  considerations  govern 
the  cost  of  the  generating  station,  as,  for  instance,  the  diffi- 
culties of  preparing  a  suitable  foundation,  the  prevalence  or 
absence  nearby  of  the  particular  building  material  desired, 
the  cost  of  transporting  the  materials  of  construction  to  the 
site,  and  the  cost  of  labor  in  the  section.  The  cost  of 
buildings  involves  too  many  variable  factors  to  attempt 
here  to  give  any  hard  and  fast  rules. 

The  cost  of  machinery  includes  the  cost  of  turbines  or 
water  wheels  and  auxiliary  apparatus  pertaining  thereto, 
such  as  governors,  valves,  and  gate-controlling  devices,  the 
cost  of  generators  and  station  apparatus.  The  cost  of  water 
wheels  varies  from  $2.50  to  $7.50  per  horse-power  out- 
put, depending  upon  their  capacity. 

In  general,  the  cost  per  kilowatt  of  generated  power 
varies  from  $100  to  $250  p»  '  -"Hill"1- 

The  Sault  Ste.  Marie  plant  complete  cost  $4,000,000,  or 


318     LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 

$135  per  kilowatt.  This  is  but  a  moderate  cost  per  unit  of 
power  compared  with  some  water-power  plants. 

The  cost  per  unit  of  power  has  many  variables,  such  as 
the  outpu*  of  the  plant,  the  conditions  of  operation,  the  cost 
of  building  material  in  the  neighborhood,  the  cost  of  labor, 
and  the  kind  of  machinery  used. 

The  cost  of  transformers  varies  directly  with  the  highest 
rate  of  transmission,  and  is  approximately  independent  of 
voltage,  the  distance  of  transmission,  and  the  line  loss. 
The  cost  of  transformers  varies  from  $6  to  $10  per  horse- 
power. For  large  capacities  a  good  average  figure  is  $7.50. 

The  cost  of  the  transmission  line  proper,  which  consists 
of  the  pole  line  and  the  conductors,  varies  according  to  the 
conditions  of  each  case.  In  the  total  cost  of  delivered 
power  the  highest  and  the  average  rates  of  power  trans- 
mitted, the  maximum  pressure  of  transmission,  the  per- 
centage of  line  loss,  and  the  distance  of  transmission,  fix 
the  ratio  of  line  cost. 

The  pole  line  varies  in  first  cost  with  the  distance  of 
transmission,  but  is  almost  unaffected  by  the  factors  above 
stated.  Since  reliability  of  operation  is  the  foremost  con- 
sideration in  long-distance  power  transmission,  a  pole  line 
of  the  stoutest  and  most  substantial  construction  is  re- 
quired. In  regions  where  timber  is  procurable  at  a  mod- 
erate cost,  the  cost  of  pole  lines,  exclusive  of  the  right  of 
way,  will  range  from  $450  to  $600  per  mile;  a  good  aver- 
age is  $525.  In  many  instances  the  right  of  way  will  cost 
nothing. 

For  a  fixed  and  maximum  percentage  of  line  loss,  the 
cost  of  conductors  varies  directly  with  the  square  of  the 
distance  of  transmission,  and  with  the  rate  of  transmitted 
power.  The  first  cost  of  conductors,  however,  decreases 


PRACTICAL    PLANTS  319 

with  increase  of  pressure,  as  the  square  of  the  voltage  of 
transmission  ;  and  also  decreases  with  increase  of  line  loss. 
Hence,  the  transmission  voltage  and  the  permissible  line 
loss  at  maximum  load  will  fix  the  weight  and  cost  of  line 
conductors. 

With  a  given  amount  of  power  to  be  transmitted,  the 
length  of  transmission  and  the  voltage,  the  weight  of  con- 
ductors required  varies  inversely  as  the  percentage  of  en- 
ergy lost  as  heat  in  the  wires.  A  fair  average  for  line 
conductors  is  from  18.5  to  20.5  cents  per  pound  for 
copper  conductors,  and  about  28.5  to  31  cents  per  pound 
for  aluminum  conductors. 

The  cost  of  operation,  which  includes  management,  labor, 
and  incidental  expenses,  repairs,  maintenance,  interest,  and 
depreciation,  will  vary  widely  with  the  circumstances  in  each 
case.  No  fixed  and  definite  figures  obtain,  since  in  each 
transmission  plant  the  cost  of  operation  is  governed  by 
different  factors.  In  general,  the  cost  of  management, 
labor,  and  incidentals  ranges  from  three  to  eight  per  cent 
yearly  on  the  total  first  cost,  depending  on  the  size  of  the 
power  development  and  the  length  of  the  transmission 
system  ;  and  hence  the  number  of  employees  required  to 
operate  it. 

The  cost  of  repairs,  maintenance,  interest,  and  deprecia- 
tion will  also  vary  with  the  size  and  length  of  the  transmis- 
sion system,  the  character  of  the  machinery  employed,  and 
the  line  construction.  The  annual  allowance  necessary  for 
repairs,  maintenance,  and  depreciation  will  vary  from  five 
to  twenty  per  cent  of  the  total  first  cost  of  the  transmission. 
Interest  charges  will  range  from  three  to  six  per  cent  per 
annum  on  the  total  investment. 

Mr.   Alton  D.  Adams  says :    "  If  a  given  amount   of 


320      LONG-DISTANCE    ELECTRIC   POWER  TRANSMISSION 

power  is  to  be  transmitted  at  a  certain  percentage  of  loss  in 
the  line,  and  at  a  fixed  voltage  over  distances  of  50,  100, 
and  200  miles,  respectively,  the  following  conclusions 
obtain  :  The  capacity  of  the  transformers  being  fixed  by 
the  rate  of  transmission  will  be  the  same  for  either  distance, 
and  their  cost  is  therefore  constant.  Transformer  losses, 
interest,  depreciation,  and  repairs  are  also  constant.  The 
cost  of  pole  lines,  depending  on  their  length,  will  be  twice 
as  great  at  100  miles,  and  four  times  as  great  at  200  as  at 
50  miles.  Interest,  depreciation,  and  repairs  will  also  go  up 
with  the  length  of  the  pole  lines. 

"  Line  conductors  will  cost  four  times  as  much  for  the  100 
mile  as  the  50  mile  transmission,  because  their  weight  will 
be  four  times  as  great,  and  the  annual  interest  and  depreci- 
ation will  go  up  at  the  same  rate.  For  the  transmission  of 
200  miles  the  cost  of  line  conductors  and  their  weight  will 
be  sixteen  times  as  great  as  the  cost  at  50  miles. 

"It  follows  that  interest,  depreciation,  and  maintenance 
will  be  increased  sixteen  times  with  the  200  mile  transmis- 
sion over  what  they  were  at  50  miles  if  voltage  and  line 
loss  are  constant." 

The  cost  of  an  electric  horse-power  hour  at  the  switch- 
board in  a  hydro-electric  station  will  differ  in  each  particular 
case,  on  account  of  the  different  outlays  required  in  hydraulic 
installations  per  unit  of  developed  power.  Where  only 
moderate  amounts  of  power  are  developed  the  cost  per 
electric  horse-power  hour  at  the  switchboard  may  range 
from  8  down  to  I  cent.  Where  large  outputs  of  power  are 
developed  the  cost  may  range  from  3  to  6  cents  per  electric 
horse-power  hour.  To  obtain  the  total  cost  of  transmission 
per  electric  horse-power,  the  percentage  found  by  dividing 
the  cost  of  operation  by  the  number  of  horse-power  hours 


PRACTICAL   PLANTS  $21 

per  annum  of  output,  must  be  added  to  the  product  obtained 
by  multiplying  the  cost  of  a  unit  of  power  at  the  switch- 
board into  the  cost  of  a  percentage  of  a  horse-power  hour 
which  is  lost  in  transmission. 

The  sum  obtained  by  adding  the  cost  of  a  unit  of  power 
at  the  switchboard,  the  cost  of  energy  transmitted,  and  the 
cost  of  the  percentage  of  a  horse-power  hour  lost  in  trans- 
mission, gives  the  total  cost  of  transmission  per  electric 
horse-power. 

The  Limitations  of  Electric  Power  Transmission.  —  Theo- 
retically, it  is  possible  to  transmit  electric  power  around 
the  globe,  provided  the  available  voltage  is  unlimited. 
Such  a  statement  follows  from  the  law  that  a  certain  amount 
of  power  may  be  conducted  to  any  distance  with  a  steady 
efficiency  and  a  predetermined  weight  of  conductors,  pro- 
vided the  pressure  of  transmission  is  increased  in  direct 
proportion  to  the  distance. 

In  practical  working,  however,  the  maximum  voltage  at 
which  it  is  safe  and  economical  to  transmit  power  is  the 
limiting  factor  in  the  present  stage  of  long-distance  power 
transmission.  The  limits  to  the  pressure  which  can  be  em- 
ployed in  practice  may  be  divided  into  several  factors  which 
enter  into  the  transmission  part  of  the  system,  per  se:  (i) 
Definite  limits  to  the  pressure  of  transmission  beyond  which 
temporary  arcing  between  the  wires  on  a  pole  will  occur, 
and  the  less  significant  but  constant  exchange  of  energy 
from  one  conductor  to  another ;  (2)  leakage  losses  through 
the  air  from  wire  to  wire  of  the  line  (see  Chapter  VI) ;  (3) 
the  necessity  of  stringing  each  wire  of  a  transmission  line 
on  a  separate  pole  line,  or  at  wider  distances  apart,  thereby 
greatly  increasing  the  cost  of  line  construction  when  press- 
ures much  higher  than  those  used  in  present  practice  are 


322     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

employed  ;   (4)  the  difficulty  of  obtaining  an  insulator  which 
is  capable  of  withstanding  very  high  pressure. 

The  first  limitation  to  high-tension  power  transmission- 
arcing,  is  caused  by  one  of  several  causes.  A  broken  or 
defective  insulator  may  give  rise  to  a  current  flow  along 
a  wet  cross-arm  from  one  conductor  to  another,  so  that  in 
time  the  wood  is  carbonized,  and  finally  a  vicious  arc  burns 
up  the  cross-arm  and  not  infrequently  the  pole  itself. 

Lines  running  in  close  proximity  to  the  sea  coast  some- 
times have  a  heavy  deposit  of  salt  formed  on  the  insulators 
and  cross-arms  which  sets  up  an  arc  between  the  conductors, 
frequently  resulting  in  the  destruction  of  the  cross-arm. 

The  same  trouble  may  occur  in  cases  where  the  line 
crosses  an  alkali  desert  or  runs  near  a  dried-up  salt  lake  or 
basin.  Arcing  troubles,  however,  are  less  frequent  in 
localities  where  the  lines  are  not  exposed  to  sea  fogs  or  salt 
dust. 

(2)  Leakage  losses  through  the  air  from  wire  to  wire  of 
a  line  directly  through  the  air  is  the  most  serious  limitation 
to  the  voltages  which  can  be  employed  with  existing  line 
construction.  The  most  notable  experimental  work  which 
has  been  thus  far  done  to  ascertain  the  rates  at  which  en- 
ergy is  lost  by  passing  through  the  air  from  wire  to  wire  of 
the  same  circuit  is  that  of  Messrs.  Scott  and  Mershon  at 
Telluride,  Colorado.  Lately  Professor  Ryan,  of  Leland 
Stanford  University  (see  Chapter  VI),  has  made  a  note- 
worthy contribution  on  the  same  subject. 

Measurements   made  by  Scott  show  that    the    leakage 
through  the  air  varies  directly  with  the  length  of  the  line, 
as  might  be  presumed.     With  fiinrkilovolts  line  pressure 
and  with  wires  15  inches  apart,  the  loss  between  wires  wasA 
approximately  1 50  watts  per  mile.     With  the  same  pressured 


PRACTICAL  PLANTS  323 

and  with  conductors  52  inches  apart,  the  loss  was  only  84 
watts  per  mile.  When  the  voltage  was  increased  to  44,000 
and  the  wires  separated  by  1 5  inches,  the  leakage  loss  was 
increased  to  nearly  413  watts  per  mile. 

At  44,000  volts  and  a  distance  of  52  inches  between 
conductors,  the  loss  was  only  94  watts  per  mile.  The 
maximum  pressure  employed  for  the  conductors  15  inches 
apart  was  47,300  volts,  at  which  the  leakage  between  the 
two  wires  became  nearly  1,215  watts  per  mile.  At  five 
kilovoltsand  a  distance  of  52  inches  between  wires  the  loss 
was  140  watts  per  mile.  As  the  pressures  increased  the 
losses  went  up  at  a  very  rapid  rate,  becoming  at  the  high- 
est voltage  measured  (59,300  volts)  nearly  1,368  watts  per 
mile. 

It  is  manifest,  if  the  leakage  losses  increase  at  a  corre- 
sponding rate  above  «yP  kilovolts,  which  is  to  be  expected, 
that  at  above- oightTfnd  a  half  kilovolts,  the  loss  will  become 
(with  wires  52  inches  apart)  more  than  7,000  watts  per 
mile.  If  such  is  the  case,  it  is  clear  that  a  long  line  at 
this  pressure  would  be  impossible.  But  to  overcome  this 
limitation  requires  only  that  the  electrical  resistance  of  the 
air  be  increased  by  stringing  the  wires  of  the  circuit  at 
greater  distances  apart.  At  the  present  time  the  greatest 
distance  apart  of  the  conductors  of  a  transmission  line  is 
78  inches,  the  three  wires  of  a  single  circuit  being  strung 
on  one  pole  line.  There  is  no  reason  why  this  distance 
cannot  be  considerably  increased  if  the  conditions  demand. 

(3)  Increased  difficulties  and  expense  of  line  construc- 
tion when  pressures  above  seven  kilovolts  are  employed. 
From  what  has  been  said  concerning  line  leakage  it  is  clear 
that  if  pressures  above  seven  or  eigM  kilovolts  are  employed, 
the  present  general  practice  of  stringing  wires  will  have  to 


324     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

be  radically  modified.  In  present  practice,  the  two  or 
three  conductors  of  a  transmission  line  are  carried  on  a 
single  pole  line,  or  in  a  number  of  instances,  several  circuits 
are  carried  on  the  same  pole  line. 

Although  the  method  of  stringing  each  wire  on  a  single 
pole  line  could  be  carried  up  to  a  limit  of  perhaps  eleven 
feet  between  any  single  wire  of  a  circuit,  the  cost  of  the 
large  poles  demanded  would  increase  the  expense  of  line 
construction  enormously.  Moreover,  at  pressures  of  about 
letfLp  or  i«i  kilovolts  this  mode  of  line  construction  would 
not  reduce  the  leakage  losses  to  a  permissible  value. 

It  is  not  improbable  that  when  line  pressures  a  few  tens 
of  kilovolts  higher  than  present  practice  come  into  use, 
each  conductor  of  a  circuit  will  be  carried  on  a  separate 
pole  line.  Since  the  distance  between  wires  with  such 
radical  line  construction  could  be  made  of  any  desirable 
value  the  losses  by  leakage  through  the  air  would  be 
negligible  regardless  of  the  voltage  of  transmission.  It 
would  seem  that  the  use  of  steel  towers  for  carrying  the 
conductors  offers  the  best  solution  to  this  limitation. 

(4)  The  difficulties  of  obtaining  an  insulator  which  will 
not  break  down  under  the  severe  stresses  of  high  potentials 
impose  another  limitation  upon  the  pressure  permissible  in 
power  transmission.  Although  at  the  present  time  insu- 
lators have  been  developed  which ^/ill  safely  and  satisfactorily 
withstand  pressures  of  over  'fifteen  kilovolts  in  laboratory 
tests,  it  remains  to  be  seen  what  will  be  their  behavior 
when  called  upon  to  insulate  a  transmission  line  under  the 
trying  conditions  of  actual  practice. 

The  principal  shortcoming  of  high-potential  insulators 
is  their  relatively  low  surface  resistance  as  compared  with 
the  body  of  the  insulator,  which  results  in  insidious  break- 


PRACTICAL   PLANTS  325 

downs  due  to  arcs  between  the  insulator  pin  and  the  cross- 
arm. 

As  the  voltage  of  transmissions  has  gone  up,  the  length 
of  insulator  pins  has  been  gradually  increased,  so  that  in 
some  transmissions  of  the  present  day  a  distance  of  nine 
or  ten  inches  between  the  lower  wet  edge  of  the  insulator 
and  cross-arm  has  been  attained.  It  is  feasible  by  using 
still  longer  pins  and  umbrella-type  insulators  of  a  larger 
size  to  increase  this  striking  distance  to  at  least  two  feet, 
at  which  distance  breakdowns  from  this  cause  would  be 
nearly  unknown. 

Some  experimental  work  has  been  done  to  discover  a 
dielectric  which  will  fulfill  the  exacting  requirements  of  line 
insulation  to  a  higher  degree  than  porcelain,  although  at 
the  present  time  it  seems  unlikely  that  the  desideratum 
will  be  found.  At  the  least,  the  insulator  problem  is  a  less 
serious  limitation  to  high-pressure  transmission  than  leak- 
age losses  from  bare  conductors. 

BIBLIOGRAPHY 

Evolution  in  High  Voltage  Transmission.  —  Scott.  Electrical  Review, 
N.  Y.,  Jan.  10,  1903. 

Costs  of  and  Losses  in  Electric  Power  Transmission.  — Adams.  Mines 
and  Mining,  N.  Y.,  Feb.,  1903. 

Does  Transmission  Pay  ?  —  Journal  of  Electricity,  Power,  and  Gas, 
San  Francisco,  Feb.,  1903,  p.  136. 

Depreciation  of  Plants.  —  Electrical  World  and  Engineer,  N.  Y., 
Nov.  17,  1900. 

Organization  of  the  Operative  Forces  of  a  Transmission  Plant.  — 
Hancock.  Journal  of  Electricity,  Power,  and  Gas,  San  Francisco,  August, 
1903,  p.  277. 

Regulation  of  a  Transmission  System  for  any  Load  and  Power 
Factor.  —  Baum.  Electrical  World  and  Engineer,  May  18,  1901,  p.  822. 


CHAPTER  XI 

DISTINCTIVE    FEATURES    OF    PROMINENT    LONG- 
DISTANCE ELECTRIC  POWER  TRANSMISSIONS. 

THE  SNOQUALMIE  FALLS  PLANT 

THIS  is  a  20,000  horse-power  transmission  from  the  falls 
of  the  Snoqualmie  River  to  Seattle,  Washington,  about  25 
miles  distant,  and  Tacoma,  44  miles  distant.  The  falls 
have  a  vertical  drop  of  270  feet,  which  is  greater  by  over 
100  feet  than  the  falls  of  Niagara.  The  water-shed  sup- 
plying the  river  is  over  500  square  miles  in  area,  and  con- 
tains numerous  mountain  lakes  and  natural  basins,  which 
it  is  possible  to  utilize  when  the  present  power  development 
is  increased  to  meet  future  demands.  The  river  does  not 
Ireeze  during  the  winter  months,  and  hence  the  plant  is 
free  from  the  serious  difficulties  encountered  in  many  other 
plants,  from  anchor  or  floating  ice. 

The  most  distinctive  feature  of  the  power  development 
is  the  location  of  the  plant  in  a  subterranean  chamber. 
The  reason  for  this  lies  in  the  fact  that  the  great  volume 
of  spray  at  the  base  of  the  falls  would  have  kept  the  build- 
ing and  apparatus  damp  during  the  summer  season,  while 
in  winter  the  coating  of  ice  on  the  building  would  have 
been  a  serious  disadvantage. 

The  water  is  conducted  directly  into  an  intake  constructed 
of  steel  and  concrete,  and  extending  about  60  feet  along 
the  river  bed.  To  prevent  floating  timber  and  driftwood 
from  entering  the  intake  the  front  is  guarded  by  a  grating 

326 


PROMINENT  POWER  TRANSMISSONS  327 

of  12  inch  by  12  inch  timbers  placed  horizontally  with 
1 2  inch  spaces  between  them  ;  the  whole  is  supported  by 
an  iron  girder  frame  made  into  the  masonry. 

The  subterranean  power  house  is  located  about  300  feet 
above  the  falls,  at  which  point  a  shaft  10  feet  by  27 
feet  was  sunk  in  the  bed  of  the  river  to  the  water  level 
below  the  falls.  From  the  face  of  the  ledge  below  the 
falls  to  the  bottom  of  the  shaft,  a  tunnel  650  feet  long  and 
12  feet  by  24  feet  in  cross-section  was  excavated.  This 
tunnel  extends  under  the  bottom  of  the  subterranean 
chamber  and  forms  the  tailrace.  The  power  house  is  a 
chamber  dug  into  the  rock  formation  and  is  350  feet  long, 
40  feet  wide,  and  30  feet  high.  Ventilation  of  the  chamber 
is  accomplished  by  the  natural  draft  through  the  tailrace. 

The  mean  temperature  of  the  chamber  is  55°  F.  which 
is  very  favorable  to  high  generator  efficiency. 

The  main  wheel  units  in  the  plant  are  probably  the 
largest  and  most  powerful  of  the  tangential  type  which 
have  ever  been  operated  under  the  same  head.  The  origi- 
nal installation  consisted  of  four  2,000  horse-power  units. 
The  wheels  are  of  the  type  (Doble  tangential)  described 
in  Chapter  III. 

The  water-distributing  receiver  is  48  inches  inside  dia- 
meter and  20  feet  8  inches  in  length,  and  is  constructed  of 
marine  steel  plates  \  inch  thick  with  dished  heads.  The 
shell  is  constructed  of  two  plates  10  feet  wide  and  suffi- 
ciently long  to  make  a  cylinder  with  only  one  longitudinal 
seam,  which  is  double  riveted.  All  flanges  are  of  semi-steel. 
The  distributing  receiver  stands  directly  over  the  foun- 
dation and  is  held  in  position  by  six  regulating  nozzles, 
which  are  mounted  in  a  vertical  plane  upon  the  foundation. 
Thus  the  water  is  delivered  from  the  receiver  into  the 


328      LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

nozzles  without  undergoing  any  change  in  direction.  The 
nozzles  are  curved  so  as  to  direct  the  water  upward 
against  the  wheels.  Each  nozzle  is  fitted  with  two  tips, 
the  diameter  of  the  jet  discharged  from  each  being  3^ 
inches. 

The  auxiliary  wheels  for  driving  the  exciters  are  also  of 
the  tangential  ellipsoidal  type.  They  are  mounted  in  steel 
housings  and  are  supplied  with  water  through  a  regulating 
nozzle  which  gives  a  jet  of  3  inches  diameter.  The  regu- 
lating nozzles  are  so  constructed  that  by  merely  opening 
the  nozzle  to  the  maximum  diameter  any  trash  or  foreign 
matter  which  may  have  lodged  in  the  nozzle  is  immediately 
washed  out,  and  the  nozzle  can  be  adjusted  to  the  proper 
jet  diameter. 

There  are  seven  generators  in  the  plant,  four  of  which 
generate  three-phase  current  at  1,000  volts  and  60  cycles. 
The  other  three  machines  are  each  of  3,000  kilowatts  out- 
put and  generate  three-phase  current  at  1,100  volts  and 
60  cycles. 

The  E.M.F.  is  raised  to  30,000  volts  by  oil-insulated, 
water-cooled  transformers,  delta  connected  on  both  the 
primary  and  secondary  sides.  Nine  of  these  transformers 
are  of  1,000  kilowatts  capacity  and  weigh  11,000  pounds 
each ;  and  each  requires  500  gallons  of  oil. 

The  switchboard  consists  of  fourteen  panels  of  white 
marble  with  separate  generating  and  multiplying  panels. 

The  poles  for  the  transmission  line  are  of  cedar,  stripped 
of  the  bark,  and  either  tarred  or  burnt  at  the  butts.  Their 
average  length  is  36  feet,  but  this  varies  with  the  contour 
of  the  country;  the  maximum  length  being  154  feet. 
Where  the  lines  cross  the  channel  in  the  harbor,  the 
poles  are  1 54  feet  long,  47  inches  in  diameter  at  the 


PROMINENT    POWER   TRANSMISSIONS  329 

butt,  and  23  inches  at  the  top,  and  weigh  2,500  pounds 
each. 

The  line  is  in  duplicate  and  is  carried  through  a  right  of 
way  averaging  50  feet  in  width.  In  some  sections  of  tim- 
ber land  the  company  has  a  right  of  way  extending  300 
feet  on  each  side  of  the  line,  through  which  sections  trees 
of  over  300  feet  in  height  had  sometimes  to  be  felled  in 
order  to  insure  immunity  from  injury  to  the  line. 

Two  circuits  are  strung  on  each  pole  line,  one  on  each 
side,  with  a  triangular  spacing  of  30  inches  between  con- 
ductors. Cross-arms  are  4^  inches  by  6  inches  and  8  and 
10  feet  long.  On  all  turns  and  crossings  double  cross- 
arms  are  used.  Four  conductors  are  strung  on  the  lower 
cross-arm,  the  inner  two  of  which  are  75  inches  from  the 
center  of  the  pole  and  the  outer  two  25  inches  from  these. 
The  upper  cross-arm  is  25.5  inches  above  the  lower  arm, 
and  on  it  are  strung  two  wires,  each  40  inches  from  the 
pole  center. 

The  conductors  are  of  stranded  aluminum,  and  about 
125  tons  of  metal  were  required  for  constructing  one  of 
the  lines.  Triple-petticoat  porcelain  insulators  are  used 
throughout.  Each  insulator  is  4.5  inches  in  height  and 
6.5  inches  in  diameter  and  weighs  four  pounds.  The  insu- 
lator pins  are  of  locust  wood  boiled  in  paraffine.  The 
distance  from  the  lower  edge  of  the  insulator  to  the  cross- 
arm  is  four  inches. 

The  length  of  span  on  the  circuit  to  Seattle  ranges 
from  90  to  150  feet,  the.  average  being  no  feet.  The 
sag  between  spans  is  about  15  inches,  which  is  much 
greater  than  is  permissible  with  copper  conductors. 

Transpositions  divide  the  line  into  six  equal  sections  ; 
the  spans  in  which  the  transpositions  are  made  are  hung 


330     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

between  two  poles  6  feet  apart.  Where  transpositions  are 
made  the  circuits  are  given  a  third  of  a  turn  always  in  the 
same  direction. 

A  telephone  line  of  No.  10  B.  &  S.  gauge  aluminum  wire 
is  carried  on  the  same  pole  line  with  one  of  the  power  cir- 
cuits, at  a  distance  of  about  5  feet  below  the  power  wires. 
At  every  fifth  pole  the  telephone  circuit  is  transposed. 

In  common  with  most  Western  long-distance  power 
transmission  systems  the  lines  are  patrolled,  each  patrol- 
man having  a  ten-mile  stretch  to  inspect  and  report  its 
condition  to  the  sub-stations  from  booths  located  every 
three  miles. 

The  power  is  utilized  in  coal-mining  operations  along  the 
route  of  the  transmission  line,  and  in  lighting  several  small 
towns.  The  greater  part  of  the  energy  is  supplied  to  the 
cities  of  Seattle  and  Tacoma,  where  it  is  consumed  by 
manufacturing  and  street  railway  properties,  etc. 

The  Missouri  River  Power  Company. — This  transmission 
plant  enjoys  the  distinction  of  being  the  first  to  employ  a 
potential  of  50,000  volts  and  at  the  present  time  is  trans- 
mitting power  at  57,000  volts.  Current  is  also  generated 
at  1 2,000  volts  for  supplying  a  small  distribution  area. 

The  power  plant  is  located  on  the  Missouri  River  near 
Canyon  Ferry  (Mont.)  and  is  17  miles  from  Helena  and  65 
miles  from  Butte.  A  dam  900  feet  long  was  constructed 
across  the  river  at  a  point  where  the  walls  of  a  canyon 
rise  to  a  considerable  height.  The  main  dam  is  built  up  of 
earth  with  a  core  wall  of  masonry,  located  on  the  east  side 
of  the  river.  The  auxiliary  dam  is  a  rock-filled,  timber  crib 
structure  with  masonry  abutments.  The  east  abutment  is 
about  325  feet  from  the  east  bank;  and  between  the 
abutment  is  a  free  spillway  472.75  feet  in  length.  From 


PROMINENT    POWER   TRANSMISSIONS  331 

the  west  abutment,  a  masonry  bulkhead  extends  90  feet  to 
an  almost  vertical  cliff. 

The  dam  forms  a  reservoir  of  about  7  miles  length  and 
over  6  square  miles  area. 

The  main  power  house  is  228  feet  in  length  and  50  feet 
in  width,  and  is  constructed  of  granite  masonry  with  steel 
roof  trusses  and  corrugated  iron.  It  contains  a  gallery  18 
feet  wide  which  extends  throughout  the  building  on  the 
west  side,  and  has  floors  of  steel  and  concrete  construction. 
The  masonry  used  throughout  the  work  was  obtained 
from  the  region  and  cut  near  the  site. 

Tt  contains  a  gallery  18  feet  wide,  which  extends  through- 
out the  building  on  the  west  side,  and  has  floors  of  steel 
and  concrete  construction. 

Water  for  operating  the  turbines  is  conducted  to  the 
power  house  through  a  canal  275  feet  long  and  54  feet 
wide.  The  canal  wall  is  constructed  of  thick  granite 
masonry  and  is  lined  throughout  with  Portland  cement. 
The  head  gates  are  electrically  operated  by  a  very  in- 
genious mechanism,  consisting  of  a  car  moving  over  rails 
laid  over  the  east  wall  of  the  canal,  and  equipped  with  the 
controlling  mechanism  ;  the  clutches  are  lever  operated  and 
the  car  is  equipped  with  a  ten  horse-power  direct-current 
motor,  receiving  current  from  an  overhead  wire  through 
the  medium  of  a  trolley  wheel.  The  car  rails  are  so  de- 
signed that  they  support  the  car  only  when  it  is  traveling 
between  gates,  or  when  it  is  throwing  pinions  into  or  out 
of  mesh  with  the  racks  on  the  gate-lifting  bars. 

The  hydraulic  equipment  of  the  plant  consists  of  ten 
pairs  of  McCormick  turbines,  two  single  turbines,  and  one 
pair  of  small  units  for  driving  the  exciters.  Each  shaft  of 
the  main  turbines  has  two  water  bearings,  one  of  which  is 


332     LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

at  the  outside  of  the  turbine  on  the  canal  side,  and  the 
other  inside  the  draft  chest.  Another  thrust  bearing  of 
the  ring-oiling  type  is  placed  outside  of  the  wheel  case, 
close  to  the  generator  coupling,  and  has  two  solid  project- 
ing rings,  fitting  into  grooves  in  the  surface  of  the  bearing. 
All  of  the  turbines  are  controlled  by  Lombard  governors. 
The  machines  discharge  their  water  into  central  cast-iron 
draft  chests,  and  thence  through  elliptical  draft  tubes  into 
the  tail  race. 

The  generator  equipment  consists  of  ten  revolving  arma- 
ture, 750  kilowatt,  three-phase,  550  volt,  60  cycle  machines, 
each  direct  connected  to  a  pair  of  turbines  by  means  of 
flexible  couplings.  Exciting  current  is  supplied  by  four 
150  volt  direct-current  generators,  one  of  which  is  coupled 
to  an  induction  motor,  and  the  other  three  directly  con- 
nected to  24  inch  turbines. 

The  switchboards  and  the  raising  transformers  for  the 
12,000  volt  service  are  installed  on  the  gallery  floor.  There 
is  a  separate  panel  for  each  generator,  and  each  machine  is 
wired  directly  to  its  panel  on  the  board. 

For  the  57,000  volt  service  there  aresix  raising  transform- 
ers, each  of  950  kilowatts  capacity  and  of  the  oil-insulated, 
water-cooled  type,  cooled  by  water  from  the  canal. 

They  are  installed  in  a  transformer  room  between  the 
wall  of  the  power  house  and  the  east  wall  of  the  canal,  and 
are  arranged  in  two  groups  with  delta  connection.  The 
protective  apparatus  for  the  57,000  volt  transformers  con- 
sists of  lightning  arresters  combined  with  static  interrupt- 
ers. Each  lightning  arrester  consists  of  114  units  with 
six  small  gaps,  and  a  large  adjustable  gap  close  to  the  line. 

High-tension  switches  between  the  two  57,000  volt 
circuits  are  designed  so  that  both  groups  of  transformers 


PROMINENT    POWER  TRANSMISSIONS  333 

may  be  put  into  joint  operation  on  one  or  both  lines ;  or 
one  group  of  transformers  may  be  used  to  operate  both 
circuits. 

The  57,000  volt  main  conductors  in  the  station  are 
800,000  circular  mill  cable  with  rubber  insulation  and  ex- 
ternal lead  sheath.  The  line  conductors  for  the  57,000 
volt  circuit  are  bare  copper  cables,  each  composed  of  seven 
strands.  The  circuit  is  strung  in  the  form  of  an  equilateral 
triangle  with  conductors  78  inches  apart,  two  wires  being 
carried  on  the  cross-arm  and  the  third  at  the  top  of  the 
pole.  The  insulator  pins  are  of  white  oak,  kiln  dried  and 
boiled  in  paraffine.  For  insulation  of  the  circuits  depend- 
ence is  placed  entirely  upon  the  insulators,  sleeves,  and 
pins. 

Transpositions  on  each  of  the  main  circuits  are  made  at 
average  distances  of  thirteen  miles,  making  five  transposi- 
tions to  Butte,  and  giving  two  complete  turns  between  the 
power  plant  and  the  Butte  sub-station. 

A  telephone  line  is  carried  on  pony  glass  insulators,  5^ 
feet  below  the  power  circuit  cross-arm,  and  is  transposed 
every  fifteen  poles. 

The  main  circuits  are  carried  over  a  right  of  way  200 
feet  wide  for  the  greater  portion  of  the  distance,  and  all 
trees  and  brush  for  a  distance  of  50  feet  on  either  side  of 
the  line  are  cleared  away. 

The  1 2,000  volt  transmission  carrying  4,000  horse-power 
is  mainly  utilized  by  smelting  works  at  Helena  seventeen 
miles  distant.  The  remainder  of  the  medium  tension 
transmission  supplies  the  incandescent  and  arc  lighting, 
street  railway  and  manufacturing  properties  of  Helena. 

The  57,000  volt  transmission  to  Butte,  aggregating  about 
8,000  horse-power,  is  consumed  principally  by  the  large 


334    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

Anaconda  mine.  Power  is  also  supplied  to  various  manu- 
facturing interests. 

The  Bay  Counties  Power  Company  of  California.  —  This 
transmission  system  is  the  longest  in  existence  and  was 
first  put  in  operation  on  April  27,  1901.  The  company  sup- 
plies power  from  three  plants  operated  in  parallel.  Power 
is  transmitted  at  40,000  volts  to  Oakland,  a  distance  of  142 
miles  from  the  main  generating  station  ;  and  power  is  sup- 
plied to  the  Standard  Electric  Company,  for  transmission 
to  various  points  along  San  Francisco  Bay,  the  farthest  of 
which  is  Stockton,  218  miles  distant  from  the  main  power 
plant. 

The  main  power  plant  of  the  system  is  located  at  Colgate, 
on  the  north  Yuba  River.  At  a  point  about  eight  miles 
above  the  power  house  a  dam  was  constructed  across  the 
river.  Thence  the  water  is  conducted  through  a  flume  to 
a  point  about  700  feet  above  the  power-house  structure. 
The  flume  system  is  laid  on  a  gradient  of  1 3  feet  to  the 
mile  and  has  a  nominal  capacity  of  20,000  miner's  inches. 
The  flume  is  about  7  feet  wide  and  5f  feet  deep  and  is 
supported  on  trestles  averaging  8f  feet  in  height.  At  the 
pony-  v,  here  the  flume  system  ends,  five  pipe  lines  conduct 
the  water  down  the  mountain  side  to  the  distributing  re- 
ceiver in  the  power  house. 

The  five  p;pe  lines  are  each  30  inches  in  diameter,  made 
of  cast  iron  at  the  bottom  and  steel  at  the  top,  and  anchored 
in  massive  concrete  blocks.  At  the  foot  of  the  pipe  lines 
is  a  massive  penstock  or  water  receiver,  which  distributes 
the  water  to  the  water  wheels  under  a  head  of  702 
feet. 

The  power-house  structure  is  located  at  the  base  of  the 
mountain  and  is  275  feet  long  and  40  feet  wide.  It  is  con- 


PROMINENT    POWER  TRANSMISSIONS  335 

structed  of  '  ttive  rock  with  steel  roof  trusses  and  corru- 
gated iron  covering. 

There  are  at  the  present  writing  seven  hydraulic  units 
installed,  consisting  of  three  3,000  horse-power  Risdon 
wheels,  and  four  1,500  horse-power  wheels,  all  of  the  tan- 
gential type.  In  addition  to  the  main  water  wheels  there 
are  two  50  horse-power  wheels  for  driving  the  exciters. 
All  units  are  direct  connected,  and  the  shafts  of  the  larger 
units  (and  the  larger  generators)  have  a  flange  at  each  end 
for  leather  link  driving.  This  arrangement  permits  any 
generator  to  be  driven  by  either  of  two  water-wheels,  with 
the  exception  of  the  outer  generator  and  water  wheel  units. 
The  smaller  units  are  independent  of  one  another,  and  each 
is  coupled  to  its  respective  wheel  through  flexible  couplings. 

The  generating  equipment  of  the  power  house  consists 
of  three  2,200  kilowatt,  three-phase,  60  cycle  Stanley  in- 
ductor alternators,  each  direct  connected  to  a  3,000  horse- 
power wheel;  and  four  1,125  kilowatt  generators,  each 
driven  by  a  1,500  horse-power  wheel. 

The  raising  transformers  are  of  the  oil-insulated,  water- 
cooled  type,  and  are  installed  in  the  main  power  house. 

The  transmission  line  for  the  142  mile  circuit  is  in  dupli- 
cate and  is  carried  on  cedar  poles  with  fir  cross-arms.  The 
average  length  of  span  is  132  feet.  The  insulator  pins  are 
mainly  of  eucalyptus  wood,  although  on  some  parts  of  the 
system  locust  is  used.  The  insulators  are  of  porcelain 
and  the  special  design  of  Mr.  R.  H.  Sterling,  superin- 
tendent of  the  Bay  division.  The  upper  part  is  of  porcelain 
with  a  very  wide  lip,  and  cemented  on  to  a  glass  insulator 
with  a  long  petticoat  by  means  of  a  sulphur  cement. 

One  of  the  transmission  circuits  is  composed  of  three 
No.  oo  hard-drawn  copper  wires,  strung  in  the  form  of  an 


336    LONG-DISTANCE    ELECTRIC    POWER   TRANSMISSION 

equilateral  triangle  with  36  inches  space  between  wires. 
Line  joints  on  the  copper  circuits  are  of  the  regular  West- 
ern Union  type  with  nine  wraps  on  each  side  and  soldered 
the  entire  length.  The  other  circuit,  which  is  strung  par- 
allel to  the  copper  line,  is  composed  of  three  No.  oooo, 
seven-strand  aluminum  cables  with  joints  of  the  thimble 
form.  Both  circuits  are  transposed  every  mile  by  making 
one  third  of  a  turn. 

The  Hudson  River  Water  Power  Company.  —  The  power 
house  is  392  feet  long  and  71  feet  wide  with  a  space 
28  feet  by  34  feet  omitted  at  one  corner.  Extending 
across  the  entire  width  of  the  structure  and  40  feet  in  the 
direction  of  its  length  is  a  compartment,  in  which  are  installed 
the  transformers  and  the  high  and  low-tension  switch- 
boards. The  remainder  of  the  structure  is  divided  into 
two  sections  in  the  lengthwise  direction  by  a  water-tight 
brick  wall  which  gives  the  wheel  chamber  a  width  of  34 
feet  and  the  generator  chamber  a  width  of  35  feet.  Ten 
steel  penstocks  each  12  feet  in  diameter  enter  from  the 
canal  along  the  outside  wall  of  the  canal.  The  water 
supply  from  eight  of  these  penstocks  drives  a  pair  of  hori- 
zontal turbine  wheels  that  discharge  through  a  single  draft 
tube,  and  are  coupled  direct  to  a  2,500  kilowatt  generator. 
The  other  two  penstocks  supply  each  one  pair  of  wheels 
direct  connected  to  a  2,000  kilowatt  generator  and  also  a 
wheel  coupled  to  a  200  kilowatt  exciter  dynamo. 

The  power  house  has  a  basement  in  that  part  in  which 
are  installed  the  transformers  and  switchboards,  with  the 
dam  as  one  of  its  side  walls.  The  basement  contains  a 
central  air  chamber  wherein  are  installed  blowers  which 
maintain  a  pressure  of  five  eighths  ounce  per  square  inch 
for  cooling  the  transformers  on  the  floor  above. 


PROMINENT   POWER   TRANSMISSIONS  337 

The  low  and  high-tension  switchboards  are  installed  at 
opposite  sides  of  this  air  chamber.  The  switching  on 
the  high-tension  board  is  performed  by  motor-operated  oil 
switches,  the  legs  of  which  are  contained  in  separate  brick 
compartments.  The  30,000  volt  connections  are  fastened 
on  the  stone  and  concrete  masonry  by  means  of  porcelain 
insulators.  For  this  purpose  each  insulator  is  fastened  to 
an  iron  pjn  and  has  a  cast-iron  top  or  cap.  The  point  be- 
tween the  pin  and  the  insulator  and  also  the  point  between 
the  insulator  and  the  iron  cap  are  made  with  a  thin  mortar 
of  Portland  cement. 

The  step-up  transformer  equipment  is  entirely  of  the  air- 
blast  type,  and  each  unit  is  designed  to  operate  at  2,000 
volts  primary  and  either  1 5,000  or  30,000  volts  secondary. 
The  transformers  are  connected  in  groups  of  three  to  a 
generator  unit. 

Lightning  arresters  for  protecting  the  transformers  are 
installed  in  stone  and  brick  cells,  each  unit  in  a  separate 
cell.  Each  conductor  of  the  transmission  circuit  is  con- 
nected to  an  arrester  plate  through  a  knife  switch. 

The  transmission  line  is  carried  on  chestnut  poles  of  a 
standard  length  of  3  5  feet  and  regularly  spaced  I  oo  feet 
apart.  On  curves  and  turns  the  pole  tops  are  pulled  over 
6  to  12  inches  by  guy  wires  made  of  seven-strand  No.  12 
B.W.G.  galvanized  steel  wire  having  a  maximum  tensile 
strength  of  80,000  pounds.  On  some  angles  pole  braces 
not  under  22  inches  in  circumference  at  their  tops  are 
employed. 

The  standard  cross-arms  used  are  i  oj  feet  long,  4  inches 
thick,  and  6  inches  deep.  Each  arm  is  given  two  coats  of 
metallic  paint.  Each  cross-arm  is  fastened  to  the  pole  by 
a  single  through  bolt  J  inches  in  diameter  and  galvanized. 


338       LONG-DISTANCE  ELECTRIC  POWER  TRANSMISSION 

The  bolt  has  a  thread  cut  over  4  inches  of  its  length  and 
is  used  with  its  nut  next  to  the  cross-arm  with  galvanized 
washers  under  both  head  and  nut.  Each  cross-arm  is 
braced  with  a  single  piece  of  galvanized  iron  bent  into  bow 
form. 

The  insulator  pins  are  of  iron.  Two  types  are  employed, 
one  for  the  straight  runs  and  the  other  for  curves  and 
corners.  The  pin  for  straight  lengths  of  line  is  constructed 
of  a  malleable  iron  casting  with  f  inch  wrought  iron  or  steel 
stud  screwed  into  its  base.  The  stud  goes  through  the 
cross-arm,  and  the  casting  is  mounted  on  the  arm  and 
carries  the  insulator.  On  curves  and  turns  a  bolt  is  passed 
entirely  through  the  cast-iron  part  of  the  pin  and  is  thence 
passed  down  through  the  arm  with  a  nut  and  washer  under- 
neath. The  length  of  the  f  inch  through  bolt  for  this 
strain  pin  is  about  16^  inches;  the  length  of  the  cast-iron 
section  mounted  above  the  cross-arm  is  8f  inches ;  the 
flange  of  the  casting  that  rests  on  the  arm  is  3|  inches  by  5 
inches  ;  the  top  of  this  casting  is  if  inches  in  diameter  with 
£  inch  threads  for  the  insulator. 

Two  types  of  porcelain  insulators  with  brown  glaze  are 
used.  The  form  most  largely  used  is  molded  in  a  single 
piece  with  double  petticoats.  The  newer  type  of  insulator 
is  made  in  three  parts  and  then  cemented  together.  The 
insulators  are  fastened  to  the  pins  by  Portland  cement 
poured  into  the  pin  hole  of  the  insulator  while  the  free  pin 
top  is  held  in  a  central  position.  The  line  wires  are  tied 
to  the  sides  of  the  insulators,  but  the  insulators  are  designed 
for  either  top  or  side  tying. 

The  line  conductors  are  made  up  of  solid,  hard-drawn 
bare  copper  of  98.5  per  cent  conductivity.  One  of  the 
three-phase  circuits  from  the  Spier  Falls  plant  contains 


PROMINENT   POWER  TRANSMISSIONS  339 

three  four-pin  cross-arms  per  pole  with  wires  spaced  36 
inches  apart.  Two  conductors  of  a  circuit  are  mounted  on 
the  two  insulators  which  are  on  that  half  of  a  top  cross-arm 
on  one  side  of  its  support.  The  remaining  conductor  of 
this  line  is  carried  on  the  insulator  at  the  end  of  the  next 
lower  arm  and  immediately  below  the  outer  of  the  two 
wires  of  that  line  on  the  top  arm.  This  method  of  string- 
ing leaves  the  inner  insulator  on  the  same  end  of  the 
middle  arm  and  the  two  insulators  on  the  corresponding 
end  of  the  third  or  bottom  cross-arm  for  another  three-phase 
line.  The  six  conductors  on  the  opposite  side  of  the  pole 
are  arranged  in  a  like  way. 

The  conductors  are  transposed  one  third  of  a  turn  for 
each  section  of  130  poles.  Thus  each  wire  passes  through 
a  complete  circle  every  7.5  miles,  there  being  52  poles  per 
mile  of  straight  line. 

In  crossing  several  railway  tracks  special  constructions 
are  employed.  The  poles  of  the  double  line  are  9  feet 
apart.  The  top  cross-arm  is  16  feet  in  length,  the  middle 
arm  10.5  feet,  and  the  lowest  arm  14  feet  long.  The 
towers  are  constructed  of  Georgia  pine  and  chestnut. 
Each  is  66. 5  feet  high  from  the  base  to  the  upper  side  of 
the  top  cross-arm  and  is  set  10.5  feet  in  the  earth. 
The  wood  in  the  towers  is  treated  with  carbolineum,  while 
all  plates  and  bolts  on  the  subterranean  parts  are  coated 
with  coal  tar. 

Guard  wires  are  not  used  for  lightning  protection  on  any 
of  the  transmission  lines,  and  arresters  are  employed  only 
at  the  central  stations,  sub-stations,  and  switch  houses. 

Where  the  conductors  enter  or  leave  a  generating  or 
sub-station  a  weather  shield  is  provided.  The  shield  is 
constructed  of  boards  on  the  side  of  the  structure  which 


34-O    LONG-DISTANCE   ELECTRIC    POWER  TRANSMISSION 

the  high-voltage  lines*  enter,  and  is  provided  with  an 
inclined  roof  and  gutter,  so  that  water  falling  on  the  roof 
is  conducted  off  the  sides  and  falls  clear  of  the  wires. 

At  central  stations,  sub-stations,  and  switch  houses 
throughout  the  transmission  system  the  arrangement  of 
the  circuits  and -switches  is  such  that  the  attendants  can 
connect  any  particular  generator  or  step-up  transformer 
to  any  circuit,  any  transmission  circuit  to  any  step-down 
transformer,  and  any  distribution  line  to  the  bus-bars 
supplied  from  any  generator. 

The  40,000  (nominal)  horse-power  developed  by  the 
two  plants  is  transmitted  to  Troy,  Albany,  Schenectady, 
Cohoes,  Lansingburg,  Ballston  Spa,  Saratoga,  Fort 
Edward,  Sandy  Hill,  and  Glens  Falls,  with  an  aggregate 
population  of  300,000.  The  power  is  mainly  utilized  by 
manufacturing  and  electric  railway  properties.  The 
General  Electric  Company  alone  has  contracted  for  10,000 
horse-power. 


INDEX 


Admittance,  definition,  171. 

equivalent  of  several  admittances 

in  parallel,  171. 

Aluminum,    advantages   and   disad- 
vantages as  conductor,  180. 
Area,  cross  section  of  jet,  6. 

method  of  determining  stream,  27. 
Arresters,    type    of    lightning,    148- 

152. 
use  of  choke  coils  with,  221. 

Bibliography  — 

(Chapter  II),  64. 

(Chapter  III),  108. 

(Chapter  IV),  158. 

(Chapter  V),  177. 

(Chapter  VI),  237. 

(Chapter  VII),  265. 

(Chapter  VIII),  290. 

(Chapter  IX),  310. 

(Chapter  X),  325. 
Bodies,  laws  of  falling,  2. 
Breakers,  circuit,  144-147. 
Buildings,    designs    of    for    power 
plants,  311. 

foundations  for,  311. 

materials  of  construction,  311. 

Calculation  of  75  Mile  Three-Phase 

Line,  231. 
Canals  and  conduits,  mean  velocity 

of  flow  in,  45. 
definition  of,  62. 
Missouri  River  Power  Company, 

33  i^- 
Capacity  or  condenscance,  definition 

of,  167. 

effect  of  in  circuits,  168. 
methods  of  overcoming,  168. 
Coefficient  of  contraction,  10. 
of  discharge,  n. 
of  velocity,  10. 


Conductance,  definition  of,  171. 

Conductors,  kinds  of,  178. 

devices  for  fastening  to  insulators, 
212. 

Constants,   electrical,  of  lines  Stan- 
dard Electric  Co.  of  California, 

174; 

electrical,  of  Bay  Counties  Power 
Company's  transmission  lines, 
176. 

Contraction,    influence    of    suppres- 
sion, ii. 

Converters,    definition    of    synchro- 
nous, 291. 

advantages  of  over  motor-genera- 
tors, 302,  304. 

definition  of  inverted,  291. 

determination  of  E.  M.  F.  of,  292. 

frequency,  use  of,  309. 

General  Electric,  301. 

hunting  of,  298. 

racing  of  armature,  300. 

ratios  of  conversion  and  capacity, 
294. 

starting  of,  295. 

troubles  of  high  frequency,  300. 

Westinghouse,  302. 
Copper,  advantages  of  as  conductor, 
179. 

amount  for  given  loss  on  maxi- 
mum difference  of  potential, 
1 86. 

amount  for  given  loss  on  mini- 
mum potential,  186. 
Coronal    discharges  on  high-tension 
circuits,  225. 

Ryan's  equation  for,  228. 
Cost    per  kilowatt  of  hydro-electric 
power,  317. 

Alton  D.  Adams  on  cost,  319. 

of  conductors,  319. 

of  pole  lines,  318. 


341 


342 


INDEX 


Cost, — continued. 
of  transformers,  318. 
of  water  wheels,  317. 
Sault  Ste.  Marie  plant,  317. 
Cross-arms,    methods   of   attaching, 

192. 
arrangement    of    on    curves    and 

dead  ending,  195. 
arrangement  of  on  straight  lines, 

195- 

treatment  of  before  attaching,  192. 
Current,  charging  of  Bay  Counties 

Power  Company's  line,  176. 
Cycle,  definition  of,  161. 

Dams,  types  of,  29. 
"arch,"  30. 
earthern,  31. 
"gravity,"  30. 
hydraulic  fill,  30. 
Missouri  River  Power  Co.,  330. 
pressure  on,  causes  of  failure,  32, 

33- 

requirements  of  masonry,  29, 
rock-fill,  30. 
Detectors,  ground,  152. 
connections  of,  153. 

Farad,  value  of,  167. 

micro,  value  of,  167. 
Floats,  kinds  of,  25. 

method    of    determining  velocity, 

by,  26. 
Flumes,  construction,  46. 

Francis  formula  of,  for  velocity,  26. 

of     Bay     Counties    Power    Co., 

334- 

stave  and  binder,  48. 
support  of,  47. 
waste,  49. 

Forebays,  purpose  of,  61. 
Frequency,  definition  of,  161. 
Fuses,  134-137- 
Gates,  head  of  Missouri  River  Power 

Co.,  331. 

Gauging,  method  of  determining  dis- 
charge by,  27. 

Generators,  kind  used  in  long-dis- 
tance transmissions,  109. 
efficiency  of,  114. 
inductor,  HI. 


Generators,  — continued. 

parallel  operation  of,  114, 

regulation  of,  112. 

revolving  armature,  109. 

revolving  field,  no. 

types  of  American,  117-119. 
Governors,  requisites  of  good,  79. 

electric  speed  controller  of,  82. 

induction  motor,  81. 

kinds  of,  80. 

Lyndon  "rapid,"  92. 

switchboard  control  of,  81. 

types  of  American,  83-92. 
"Grizzles,"  definition  of,  62. 
Grounding,   of  high-potential  lines, 
228. 

Head  of  water,  definition,  2. 
Hydraulic  radius,  definition  of,  23. 

machines,  efficiencies  of,  68. 

necessity  for  high  efficiency,  70. 

power  of  waterfall  utilized  by,  76. 

requirements  for  high  efficiency, 
69. 

Impedance,  definition  of,  170. 

equivalent  of  several  impedances 
in  series  and  parallel,  171. 

resultant  of  several  impedances  in 

series,  170. 

Impulse,  definition  of,  7. 
Inductance,  definition  of,  162. 

definition  of  coefficient  of,  163. 

effect  in  A.  C.  circuits,  162. 

methods  of  decreasing  self  circuits, 
1 66. 

methods  of  expressing,  164. 

methods  of  mutual  of  circuits,  166. 

mutual  of  circuits,  164. 
Instruments,    hydraulic    measuring, 
18. 

current  meter,  20. 

differential  mercury  gauge,  20. 

differential  pressure  gauge,  19. 

hook-gauge,  18. 

piezometer,  18. 

water  meter,  21. 
Insulators,  kinds  of,  205. 

advantages  of  glass,  208. 

advantages  of  porcelain,  206. 

clamp  for  standard,  213. 


INDEX 


343 


Insulators,  —  continued. 
clamp,  interlocking,  212. 
clamp,  under-locking,  213. 
combination,  208. 
Locke  high-tension,  210-211. 
"Muncie"  type,  212. 
"Provo  "  type,  211. 
testing  of,  209. 

Jet,  energy  of,  5. 
area  of,  6. 

impulse  and  dynamic  reaction  of, 
6. 

Kutter's  formula,  46. 

Lightning,  effects  of,  on  circuits,  220. 
methods  of  safeguarding  against, 

222. 

Limitations  of  electric  power  trans- 
mission, 321. 

Lines,  construction  of  pole,  189. 
factors  which  govern  design  and 
construction  of  transmission,  178. 
stresses  on  pole,  191. 
Losses,  leakage  and  electrostatic,  in 
lines,  224. 

Motor  generators,  ad  vantage  pf  over- 
converters,  304. 

efficiencies  of,  305. 
Motor  repulsion,  287. 
Motors,  behavior  of  synchronous,  on 
starting,  267. 

curves  of,  289. 

definition  of  slip,  275. 

efficiencies  of  induction,  281. 

faults  of,  282. 

features  of  squirrel-cage  induction, 
27. 

features  of  variable-resistance  in- 
duction, 275. 

General  Electric,  288. 

induction,  description"  of,  274. 

limit   of   output   of   synchronous, 
267. 

methods  of  starting  synchronous, 
267. 

power  factor,  282. 

relations  between  torque  and  slip, 
277- 


Motors,  —  continued. 

relations   between  torque,  speed, 

power,  factor,  etc.,  278. 
speed  regulation  of  induction,  278. 
synchronous,  definition  of,  266. 
theory  of  operation  of  induction, 

277. 

troubles  of  synchronous,  272. 
use    of  synchronous,   as   voltage 

regulators,  270. 
Westinghouse,  285. 

Nozzles  for  water  wheels,  75. 
deflecting,  78. 
needle  regulating,  105. 
plug,  780 

Orifices,  flow  from,  4. 
discharge  from  small,  4. 
flow  from  circular,  13. 
flow  from  rectangular  and  square 

vertical,  13. 
measurement  of  water  by,  14. 

Pins,  kinds  of  insulator,  203. 

advantage  of  metallic,  205. 

faults  of  wooden,  204. 

insulator,  of  Hudson  River  Power 
Co.,  338. 

treatment  of  wooden,  203. 
Pipe  lines,  loss  of  head  in,  37. 

cast  iron,  advantages,  54 

circumferential  pressure  in,  51. 

construction  of,  52. 

determination  of  diameter  to  dis- 
charge given  quantity  of  water, 
42. 

determination  of  discharge  from, 

_42. 

friction,  factor  of,  37. 

influence  of  contraction  of  cross 

section,  38. 
kind  of  joints  used  on  solid  metal, 

54- 

kinds  of  joints  used  on,  56. 
long  pipes,  43. 
loss  of  head  in,  39. 
maximum  energy  transmitted  by, 

44. 

mean  velocity  of  flow  in,  40. 
riveted  pipe,  55. 


344 


INDEX 


Pipe  lines, — continued. 

stove  pipe,  advantages  and  disad- 
vantages of,  53. 

method   of  anchoring  on  steep 
grades,  59. 
auxiliaries  of,  61. 
curve  factors,  40. 
loss  of  head  by  curves,  39. 
safety  devices  for,  59. 
table  of  riveted,  60. 
Pipes,  long,  43. 

expression  for  velocity  in,  43. 
stresses  in  riveted  steel,  51. 
Pole  lines,  patrolling  of,  230. 
Poles  for  transmission  lines,  187. 

sizes  of  and  setting,  188. 
Power  factor,  definition  of,  160. 
Power    house    of    Missouri    River 

Power  Co.,  331. 

of  Bay  Counties  Company  of  Cali- 
fornia, 334. 
of     Hudson      River     Company, 

33.6- 

Power  in  an  alternating  current  cir- 
cuit, 159. 

Power  plants,  arrangement  of  ma- 
chinery in,  312. 
description    of     Missouri     River 

Power  Co.,  330. 
description  of  Snoqualmie  Falls, 

326. 

parallel  operation  of,  314. 
regulation  of,  314. 
transmission,  factors  which  govern 

cost,  317. 

Power  transmission,   electrical  fac- 
tors of,  161. 
Pressure  of  water,  i. 

distinction  between  pressure  and 

head,  2. 

pressure  head,  9. 
Protective  devices,  automatic  station, 

134- 

Protection  of  transmission  lines  from 
lightning,  220. 

Reactance,  inductive,  165. 

capacity,  168. 

effect  of,  in  circuits,  165. 
Receiver,  water  distributing,  327. 
Relay,  overload,  137. 


Relay,  —  continued. 

circuit  connections  of  reverse  cur- 
rent, 143- 
construction  of  time  limit,   140- 

142. 

function  of  overload  time,  138. 
overload  time  limit,  138. 
reverse  current,  142. 
reverse  current  time  element,  143. 
Reservoirs,  storage,  34. 
Resistance,  definition  of  in  a.  c.  cir- 
cuits, 169. 
Resonance,  definition  of,  172. 

effect    of    in  series  and  parallel, 

173- 

Right  of  way  of  Snoqualmie  Falls 

Power  Co.,  327. 
of  Missouri  River  Power  Co.,  333. 

Sand  boxes,  types  of,  62. 
Scott,    Charles   F.,   investigation   of 
losses  on  high-tension  lines,  225. 
method    of    hysteresis    measure- 
ment, 246. 
Spans,  factors  which  govern  length, 

218. 

length  for  aluminum  circuits,  220. 
length  for  copper  circuits,  220. 
length  of  on  Snoqualmie  Falls  line, 

329- 

Speed  of  impulse  and  reaction  tur- 
bines, 67. 

Star  and  delta  methods  of  transfor- 
mer connections,  253. 
Static,  strains  in  transformers,  251. 

interrupters  for  protecting,  252. 
Steel-supporting  structures  for  trans 

mission  lines,  197. 
advantages  over  pole  lines,  199. 
comparison  of  cost,  200. 
types  of,  200-203. 

Steinmetz,  Charles  P., investigation  of 
losses  on  high-tension  lines,  225. 
Storage  reservoirs,  factors  which  de- 
termine size  of,  35. 
Streams,  flow  in,  23. 

definition  of  slope  of  water  surface, 

24. 

determination  of  energy  of,  24. 
equations  for  discharge,  17-28. 
hydraulic  radius  of,  23. 


INDEX 


345 


Streams,  —  continued. 

method  of  making  weir  measure- 
ments of,  17. 
willed  perimeter  of  cross  section, 

23- 
Substations,  design  of,  315. 

methods  of  conducting  current  in, 

3*5>  339- 
Surges  in  transmission  lines,  220. 

causes  of,  223—224. 
Susceptance,  definition  of,  171. 
Switchboards  for   high-tension  cur- 
rent, 119. 

instrument  equipment,  120. 

location  in  power  plants,  313. 
Switches  for  high  voltages,  122. 

oil-break,  122-129. 

air-break  with  fuse,  129. 

"rams'  horn"  air-break,  132. 
Switching,  when  necessary,  133. 
Synchronizing,  devices  for,  153. 

Lincoln  synchroscope,  155. 

principles  of  operation  of,  154. 

synchronism  indicator,  157. 

Table  of  loss  of  head  in  pipes,  41. 

riveted  hydraulic  pipe,  60. 
Transformers,  capacity  of,  243. 

comparison    between    Y    and 
A  methods  of  connection,  253. 

definition  of,  239. 

efficiencies  of,  244. 

equation  for  hysteresis  loss  in,  241 . 

Foucault  current  loss  in,  242. 

grounding,  secondaries  of,  255. 

heating,  test  of,  249. 

insulation,  test  of,  250. 

kinds  used  in  high-tension    prac- 
tice, 257. 

location  in  power  plants,  313. 

losses  in,  240. 

methods  of  installation,  256. 

methods  of  making  efficiency  tests 
of,  250. 

Stanley  water-cooled,  264. 

static  interrupters  for,  252. 

static  strains  in,  251. 

testing  of,  245. 

various  connections  of,  253. 

Westinghouse  air  blast,  262. 

Westinghouse  water-cooled,  264. 


Transpositions,  on  lines  of  Snoqual- 

mie  Falls  Power  Co.,  329. 
Turbine,  definition  of,  65. 

conditions  to  which  impulse  and 
reaction  are  adapted,  67. 

downward  flow,  66. 

"impulse"  and  "reaction,"  65. 

inward  flow,  66. 

outward  flow,  66. 
Turbines,  types  of  American,  71. 

accessories  of,  105. 

faults  of,  99. 

installation  of,  312. 

McCormick,  75. 

regulation  of  water  supply  to,  73. 

regulation  of  speed,  77. 

Samson,  71-72. 

testing  of,  98. 

Victor,  72-73. 

Valves,  gate,  105. 

safety  relief,  106. 
Velocity,  equations  for,  3. 

head,  9. 

Water  wheels,  definition  of,  65. 

accessories  of,  105. 

bucket  construction  of,  75. 

Doble,  104. 

faults  of,  99. 

impulse,  effective  headon,  77. 

Pelton,  100. 

principles  of  operation,  74. 

Risdon,  102. 

speed  regulation  of,  77. 

testing  of,  98. 

things    upon    which    speed    and 
power  depend,  76. 

types  of  American,  100-105. 
Weight  of  copper  for  various  circuits, 

182. 
WtirSj  definition  of,  14. 

equations  for  discharge  of,  36. 

forms  of,  36. 

kinds  of,  15. 

waste,  35. 

Wood,  methods  of  preserving,  195. 
Wires,  methods  of  stringing,  214. 

factors  which  govern  number  of 
transpositions,  216. 

transposition  of,  216. 


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